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 $56.80   12.232%   $63.7478   $63.75   $63.75   $63.70  
  Purchase #2 $10.51   10.661%   $11.6305   $11.63   $11.65   $11.60  
  Purchase #3 $176.94   12.185%   $198.5001   $198.50   $198.50   $198.50  
  Purchase #4 $195.97   12.217%   $219.9117   $219.91   $219.90   $219.90  
  Purchase #5 $216.38   10.371%   $238.8208   $238.82   $238.80   $238.80  
  Purchase #6 $130.67   13.187%   $147.9015   $147.90   $147.90   $147.90  
  Purchase #7 $63.81   4.556%   $66.7172   $66.72   $66.70   $66.70  
  7 purchase totals = $851.08       $947.2296   $947.23   $947.20   $947.10