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 $230.59   5.532%   $243.3462   $243.35   $243.35   $243.30  
  Purchase #2 $88.53   6.508%   $94.2915   $94.29   $94.30   $94.30  
  Purchase #3 $24.52   5.761%   $25.9326   $25.93   $25.95   $25.90  
  Purchase #4 $87.42   7.146%   $93.667   $93.67   $93.65   $93.70  
  Purchase #5 $209.58   12.715%   $236.2281   $236.23   $236.25   $236.20  
  Purchase #6 $168.93   4.186%   $176.0014   $176.00   $176.00   $176.00  
  Purchase #7 $230.84   13.160%   $261.2185   $261.22   $261.20   $261.20  
  7 purchase totals = $1,040.41       $1,130.6853   $1,130.69   $1,130.70   $1,130.60