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 $234.51   9.264%   $256.235   $256.24   $256.25   $256.20  
  Purchase #2 $33.82   4.281%   $35.2678   $35.27   $35.25   $35.30  
  Purchase #3 $241.56   5.610%   $255.1115   $255.11   $255.10   $255.10  
  Purchase #4 $200.89   13.858%   $228.7293   $228.73   $228.75   $228.70  
  Purchase #5 $43.69   10.368%   $48.2198   $48.22   $48.20   $48.20  
  Purchase #6 $219.37   4.136%   $228.4431   $228.44   $228.45   $228.40  
  Purchase #7 $228.57   9.376%   $250.0007   $250.00   $250.00   $250.00  
  7 purchase totals = $1,202.41       $1,302.0072   $1,302.01   $1,302.00   $1,301.90