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 $201.46   11.515%   $224.6581   $224.66   $224.65   $224.70  
  Purchase #2 $26.82   9.424%   $29.3475   $29.35   $29.35   $29.30  
  Purchase #3 $231.41   6.726%   $246.9746   $246.97   $246.95   $247.00  
  Purchase #4 $54.61   10.502%   $60.3451   $60.35   $60.35   $60.30  
  Purchase #5 $172.29   5.633%   $181.9951   $182.00   $182.00   $182.00  
  Purchase #6 $119.54   7.249%   $128.2055   $128.21   $128.20   $128.20  
  Purchase #7 $46.42   10.277%   $51.1906   $51.19   $51.20   $51.20  
  7 purchase totals = $852.55       $922.7165   $922.73   $922.70   $922.70