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 $117.54   11.731%   $131.3286   $131.33   $131.35   $131.30  
  Purchase #2 $196.77   3.648%   $203.9482   $203.95   $203.95   $203.90  
  Purchase #3 $150.71   10.719%   $166.8646   $166.86   $166.85   $166.90  
  Purchase #4 $240.31   10.459%   $265.444   $265.44   $265.45   $265.40  
  Purchase #5 $62.59   5.566%   $66.0738   $66.07   $66.05   $66.10  
  Purchase #6 $123.53   10.793%   $136.8626   $136.86   $136.85   $136.90  
  Purchase #7 $125.39   8.143%   $135.6005   $135.60   $135.60   $135.60  
  7 purchase totals = $1,016.84       $1,106.1223   $1,106.11   $1,106.10   $1,106.10