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 $209.43   6.253%   $222.5257   $222.53   $222.55   $222.50  
  Purchase #2 $177.40   8.869%   $193.1336   $193.13   $193.15   $193.10  
  Purchase #3 $54.33   8.379%   $58.8823   $58.88   $58.90   $58.90  
  Purchase #4 $160.83   3.221%   $166.0103   $166.01   $166.00   $166.00  
  Purchase #5 $28.75   6.679%   $30.6702   $30.67   $30.65   $30.70  
  Purchase #6 $108.99   8.777%   $118.5561   $118.56   $118.55   $118.60  
  Purchase #7 $29.87   11.129%   $33.1942   $33.19   $33.20   $33.20  
  7 purchase totals = $769.60       $822.9724   $822.97   $823.00   $823.00