Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $121.77   11.734%   $136.0585   $136.06   $136.05   $136.10  
  Purchase #2 $222.47   10.710%   $246.2965   $246.30   $246.30   $246.30  
  Purchase #3 $114.59   10.713%   $126.866   $126.87   $126.85   $126.90  
  Purchase #4 $169.60   4.206%   $176.7334   $176.73   $176.75   $176.70  
  Purchase #5 $180.49   10.864%   $200.0984   $200.10   $200.10   $200.10  
  Purchase #6 $192.85   8.651%   $209.5335   $209.53   $209.55   $209.50  
  Purchase #7 $150.31   3.116%   $154.9937   $154.99   $155.00   $155.00  
  7 purchase totals = $1,152.08       $1,250.5800   $1,250.58   $1,250.60   $1,250.60