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 $209.60   10.655%   $231.9329   $231.93   $231.95   $231.90  
  Purchase #2 $85.93   9.418%   $94.0229   $94.02   $94.00   $94.00  
  Purchase #3 $158.76   13.468%   $180.1418   $180.14   $180.15   $180.10  
  Purchase #4 $102.81   7.458%   $110.4776   $110.48   $110.50   $110.50  
  Purchase #5 $57.53   12.743%   $64.861   $64.86   $64.85   $64.90  
  Purchase #6 $200.52   3.723%   $207.9854   $207.99   $208.00   $208.00  
  Purchase #7 $68.96   12.621%   $77.6634   $77.66   $77.65   $77.70  
  7 purchase totals = $884.11       $967.0850   $967.08   $967.10   $967.10