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 $63.39   12.109%   $71.0659   $71.07   $71.05   $71.10  
  Purchase #2 $127.27   6.587%   $135.6533   $135.65   $135.65   $135.70  
  Purchase #3 $20.59   5.315%   $21.6844   $21.68   $21.70   $21.70  
  Purchase #4 $24.57   7.855%   $26.5   $26.50   $26.50   $26.50  
  Purchase #5 $76.94   9.605%   $84.3301   $84.33   $84.35   $84.30  
  Purchase #6 $137.97   10.347%   $152.2458   $152.25   $152.25   $152.20  
  Purchase #7 $163.98   4.137%   $170.7639   $170.76   $170.75   $170.80  
  7 purchase totals = $614.71       $662.2434   $662.24   $662.25   $662.30