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 $214.53   7.667%   $230.978   $230.98   $231.00   $231.00  
  Purchase #2 $61.37   4.854%   $64.3489   $64.35   $64.35   $64.30  
  Purchase #3 $56.87   6.681%   $60.6695   $60.67   $60.65   $60.70  
  Purchase #4 $162.79   4.206%   $169.6369   $169.64   $169.65   $169.60  
  Purchase #5 $11.84   12.266%   $13.2923   $13.29   $13.30   $13.30  
  Purchase #6 $30.86   11.255%   $34.3333   $34.33   $34.35   $34.30  
  Purchase #7 $235.40   5.778%   $249.0014   $249.00   $249.00   $249.00  
  7 purchase totals = $773.66       $822.2603   $822.26   $822.30   $822.20