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 $206.60   12.422%   $232.2639   $232.26   $232.25   $232.30  
  Purchase #2 $228.96   11.684%   $255.7117   $255.71   $255.70   $255.70  
  Purchase #3 $46.86   13.717%   $53.2878   $53.29   $53.30   $53.30  
  Purchase #4 $227.91   13.531%   $258.7485   $258.75   $258.75   $258.70  
  Purchase #5 $35.65   10.773%   $39.4906   $39.49   $39.50   $39.50  
  Purchase #6 $209.92   7.797%   $226.2875   $226.29   $226.30   $226.30  
  Purchase #7 $37.72   8.192%   $40.81   $40.81   $40.80   $40.80  
  7 purchase totals = $993.62       $1,106.6000   $1,106.60   $1,106.60   $1,106.60