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 $165.31   13.696%   $187.9509   $187.95   $187.95   $188.00  
  Purchase #2 $28.72   13.163%   $32.5004   $32.50   $32.50   $32.50  
  Purchase #3 $107.91   8.865%   $117.4762   $117.48   $117.50   $117.50  
  Purchase #4 $234.92   12.530%   $264.3555   $264.36   $264.35   $264.40  
  Purchase #5 $14.98   4.512%   $15.6559   $15.66   $15.65   $15.70  
  Purchase #6 $185.90   3.867%   $193.0888   $193.09   $193.10   $193.10  
  Purchase #7 $166.33   11.581%   $185.5927   $185.59   $185.60   $185.60  
  7 purchase totals = $904.07       $996.6204   $996.63   $996.65   $996.80