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 $84.86   11.779%   $94.8557   $94.86   $94.85   $94.90  
  Purchase #2 $204.78   11.293%   $227.9058   $227.91   $227.90   $227.90  
  Purchase #3 $236.32   13.546%   $268.3319   $268.33   $268.35   $268.30  
  Purchase #4 $5.34   13.140%   $6.0417   $6.04   $6.05   $6.00  
  Purchase #5 $15.75   12.628%   $17.7389   $17.74   $17.75   $17.70  
  Purchase #6 $166.77   12.207%   $187.1276   $187.13   $187.15   $187.10  
  Purchase #7 $85.59   9.797%   $93.9753   $93.98   $94.00   $94.00  
  7 purchase totals = $799.41       $895.9769   $895.99   $896.05   $895.90