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 $58.54   8.506%   $63.5194   $63.52   $63.50   $63.50  
  Purchase #2 $238.84   7.577%   $256.9369   $256.94   $256.95   $256.90  
  Purchase #3 $196.61   9.689%   $215.6595   $215.66   $215.65   $215.70  
  Purchase #4 $139.90   7.814%   $150.8318   $150.83   $150.85   $150.80  
  Purchase #5 $237.76   8.162%   $257.166   $257.17   $257.15   $257.20  
  Purchase #6 $249.40   5.629%   $263.4387   $263.44   $263.45   $263.40  
  Purchase #7 $76.73   11.601%   $85.6314   $85.63   $85.65   $85.60  
  7 purchase totals = $1,197.78       $1,293.1837   $1,293.19   $1,293.20   $1,293.10