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 $50.44   8.557%   $54.7562   $54.76   $54.75   $54.80  
  Purchase #2 $236.59   12.296%   $265.6811   $265.68   $265.70   $265.70  
  Purchase #3 $166.40   10.266%   $183.4826   $183.48   $183.50   $183.50  
  Purchase #4 $61.39   6.411%   $65.3257   $65.33   $65.35   $65.30  
  Purchase #5 $200.79   8.331%   $217.5178   $217.52   $217.50   $217.50  
  Purchase #6 $97.56   5.732%   $103.1521   $103.15   $103.15   $103.20  
  Purchase #7 $65.36   13.453%   $74.1529   $74.15   $74.15   $74.20  
  7 purchase totals = $878.53       $964.0684   $964.07   $964.10   $964.20