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 $118.35   5.751%   $125.1563   $125.16   $125.15   $125.20  
  Purchase #2 $57.53   11.114%   $63.9239   $63.92   $63.90   $63.90  
  Purchase #3 $194.63   4.469%   $203.328   $203.33   $203.35   $203.30  
  Purchase #4 $87.25   7.400%   $93.7065   $93.71   $93.70   $93.70  
  Purchase #5 $117.65   4.145%   $122.5266   $122.53   $122.55   $122.50  
  Purchase #6 $229.66   11.252%   $255.5013   $255.50   $255.50   $255.50  
  Purchase #7 $122.79   3.700%   $127.3332   $127.33   $127.35   $127.30  
  7 purchase totals = $927.86       $991.4758   $991.48   $991.50   $991.40