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 $190.30   5.795%   $201.3279   $201.33   $201.35   $201.30  
  Purchase #2 $207.66   4.275%   $216.5375   $216.54   $216.55   $216.50  
  Purchase #3 $211.74   4.279%   $220.8004   $220.80   $220.80   $220.80  
  Purchase #4 $54.65   9.231%   $59.6947   $59.69   $59.70   $59.70  
  Purchase #5 $87.29   4.426%   $91.1535   $91.15   $91.15   $91.20  
  Purchase #6 $61.38   7.677%   $66.0921   $66.09   $66.10   $66.10  
  Purchase #7 $5.95   11.398%   $6.6282   $6.63   $6.65   $6.60  
  7 purchase totals = $818.97       $862.2343   $862.23   $862.30   $862.20