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 $217.85   3.427%   $225.3157   $225.32   $225.30   $225.30  
  Purchase #2 $237.48   9.328%   $259.6321   $259.63   $259.65   $259.60  
  Purchase #3 $59.32   9.405%   $64.899   $64.90   $64.90   $64.90  
  Purchase #4 $167.80   6.302%   $178.3748   $178.37   $178.35   $178.40  
  Purchase #5 $249.97   10.333%   $275.7994   $275.80   $275.80   $275.80  
  Purchase #6 $225.50   12.472%   $253.6244   $253.62   $253.60   $253.60  
  Purchase #7 $74.52   6.427%   $79.3094   $79.31   $79.30   $79.30  
  7 purchase totals = $1,232.44       $1,336.9548   $1,336.95   $1,336.90   $1,336.90