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 $125.55   12.481%   $141.2199   $141.22   $141.20   $141.20  
  Purchase #2 $58.77   6.565%   $62.6283   $62.63   $62.65   $62.60  
  Purchase #3 $172.92   5.783%   $182.92   $182.92   $182.90   $182.90  
  Purchase #4 $166.55   7.130%   $178.425   $178.43   $178.45   $178.40  
  Purchase #5 $93.26   9.491%   $102.1113   $102.11   $102.10   $102.10  
  Purchase #6 $247.62   6.331%   $263.2968   $263.30   $263.30   $263.30  
  Purchase #7 $171.74   7.549%   $184.7047   $184.70   $184.70   $184.70  
  7 purchase totals = $1,036.41       $1,115.3060   $1,115.31   $1,115.30   $1,115.20