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 $151.41   13.104%   $171.2508   $171.25   $171.25   $171.30  
  Purchase #2 $177.83   3.503%   $184.0594   $184.06   $184.05   $184.10  
  Purchase #3 $19.46   5.381%   $20.5071   $20.51   $20.50   $20.50  
  Purchase #4 $210.45   3.519%   $217.8557   $217.86   $217.85   $217.90  
  Purchase #5 $36.44   13.371%   $41.3124   $41.31   $41.30   $41.30  
  Purchase #6 $8.84   5.747%   $9.348   $9.35   $9.35   $9.30  
  Purchase #7 $84.72   13.560%   $96.208   $96.21   $96.20   $96.20  
  7 purchase totals = $689.15       $740.5414   $740.55   $740.50   $740.60