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 $75.88   12.726%   $85.5365   $85.54   $85.55   $85.50  
  Purchase #2 $215.72   7.126%   $231.0922   $231.09   $231.10   $231.10  
  Purchase #3 $115.75   6.779%   $123.5967   $123.60   $123.60   $123.60  
  Purchase #4 $167.41   8.425%   $181.5143   $181.51   $181.50   $181.50  
  Purchase #5 $44.71   10.490%   $49.4001   $49.40   $49.40   $49.40  
  Purchase #6 $166.72   6.725%   $177.9319   $177.93   $177.95   $177.90  
  Purchase #7 $174.31   11.313%   $194.0297   $194.03   $194.05   $194.00  
  7 purchase totals = $960.50       $1,043.1014   $1,043.10   $1,043.15   $1,043.00