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 $250.39   5.291%   $263.6381   $263.64   $263.65   $263.60  
  Purchase #2 $58.49   11.659%   $65.3093   $65.31   $65.30   $65.30  
  Purchase #3 $16.45   6.466%   $17.5137   $17.51   $17.50   $17.50  
  Purchase #4 $89.80   5.799%   $95.0075   $95.01   $95.00   $95.00  
  Purchase #5 $109.73   8.470%   $119.0241   $119.02   $119.00   $119.00  
  Purchase #6 $37.67   6.444%   $40.0975   $40.10   $40.10   $40.10  
  Purchase #7 $244.76   6.846%   $261.5163   $261.52   $261.50   $261.50  
  7 purchase totals = $807.29       $862.1065   $862.11   $862.05   $862.00