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 $51.63   12.843%   $58.2608   $58.26   $58.25   $58.30  
  Purchase #2 $204.84   11.361%   $228.1119   $228.11   $228.10   $228.10  
  Purchase #3 $182.96   4.421%   $191.0487   $191.05   $191.05   $191.00  
  Purchase #4 $41.80   11.373%   $46.5539   $46.55   $46.55   $46.60  
  Purchase #5 $65.68   8.149%   $71.0323   $71.03   $71.05   $71.00  
  Purchase #6 $230.96   4.719%   $241.859   $241.86   $241.85   $241.90  
  Purchase #7 $93.65   10.764%   $103.7305   $103.73   $103.75   $103.70  
  7 purchase totals = $871.52       $940.5971   $940.59   $940.60   $940.60