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 $227.59   11.386%   $253.5034   $253.50   $253.50   $253.50  
  Purchase #2 $189.31   7.419%   $203.3549   $203.35   $203.35   $203.40  
  Purchase #3 $141.75   3.521%   $146.741   $146.74   $146.75   $146.70  
  Purchase #4 $86.73   7.840%   $93.5296   $93.53   $93.55   $93.50  
  Purchase #5 $214.33   6.462%   $228.18   $228.18   $228.20   $228.20  
  Purchase #6 $154.51   4.723%   $161.8075   $161.81   $161.80   $161.80  
  Purchase #7 $190.74   5.454%   $201.143   $201.14   $201.15   $201.10  
  7 purchase totals = $1,204.96       $1,288.2594   $1,288.25   $1,288.30   $1,288.20