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 $53.82   13.709%   $61.1982   $61.20   $61.20   $61.20  
  Purchase #2 $149.85   4.770%   $156.9978   $157.00   $157.00   $157.00  
  Purchase #3 $152.31   3.555%   $157.7246   $157.72   $157.70   $157.70  
  Purchase #4 $25.27   4.208%   $26.3334   $26.33   $26.35   $26.30  
  Purchase #5 $217.45   8.765%   $236.5095   $236.51   $236.50   $236.50  
  Purchase #6 $234.56   5.261%   $246.9002   $246.90   $246.90   $246.90  
  Purchase #7 $29.60   10.858%   $32.814   $32.81   $32.80   $32.80  
  7 purchase totals = $862.86       $918.4777   $918.47   $918.45   $918.40