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 $55.81   13.322%   $63.245   $63.25   $63.25   $63.20  
  Purchase #2 $15.43   12.258%   $17.3214   $17.32   $17.30   $17.30  
  Purchase #3 $125.40   13.455%   $142.2726   $142.27   $142.25   $142.30  
  Purchase #4 $92.29   5.404%   $97.2774   $97.28   $97.30   $97.30  
  Purchase #5 $64.78   11.498%   $72.2284   $72.23   $72.25   $72.20  
  Purchase #6 $247.69   12.121%   $277.7125   $277.71   $277.70   $277.70  
  Purchase #7 $225.99   5.507%   $238.4353   $238.44   $238.45   $238.40  
  7 purchase totals = $827.39       $908.4926   $908.50   $908.50   $908.40