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 $51.64   8.534%   $56.047   $56.05   $56.05   $56.00  
  Purchase #2 $112.90   3.245%   $116.5636   $116.56   $116.55   $116.60  
  Purchase #3 $83.92   3.625%   $86.9621   $86.96   $86.95   $87.00  
  Purchase #4 $83.41   12.553%   $93.8805   $93.88   $93.90   $93.90  
  Purchase #5 $53.78   4.810%   $56.3668   $56.37   $56.35   $56.40  
  Purchase #6 $233.70   11.646%   $260.9167   $260.92   $260.90   $260.90  
  Purchase #7 $187.36   8.226%   $202.7722   $202.77   $202.75   $202.80  
  7 purchase totals = $806.71       $873.5089   $873.51   $873.45   $873.60