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 $75.96   12.595%   $85.5272   $85.53   $85.55   $85.50  
  Purchase #2 $211.71   7.121%   $226.7859   $226.79   $226.80   $226.80  
  Purchase #3 $110.35   6.212%   $117.2049   $117.20   $117.20   $117.20  
  Purchase #4 $98.67   6.155%   $104.7431   $104.74   $104.75   $104.70  
  Purchase #5 $235.41   12.238%   $264.2195   $264.22   $264.20   $264.20  
  Purchase #6 $86.64   13.840%   $98.631   $98.63   $98.65   $98.60  
  Purchase #7 $35.40   10.203%   $39.0119   $39.01   $39.00   $39.00  
  7 purchase totals = $854.14       $936.1235   $936.12   $936.15   $936.00