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 $183.25   9.469%   $200.6019   $200.60   $200.60   $200.60  
  Purchase #2 $161.56   11.244%   $179.7258   $179.73   $179.75   $179.70  
  Purchase #3 $39.66   11.621%   $44.2689   $44.27   $44.25   $44.30  
  Purchase #4 $194.78   11.517%   $217.2128   $217.21   $217.20   $217.20  
  Purchase #5 $195.95   7.569%   $210.7815   $210.78   $210.80   $210.80  
  Purchase #6 $235.63   13.331%   $267.0418   $267.04   $267.05   $267.00  
  Purchase #7 $129.26   4.377%   $134.9177   $134.92   $134.90   $134.90  
  7 purchase totals = $1,140.09       $1,254.5504   $1,254.55   $1,254.55   $1,254.50