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 $213.97   10.418%   $236.2614   $236.26   $236.25   $236.30  
  Purchase #2 $87.72   5.624%   $92.6534   $92.65   $92.65   $92.70  
  Purchase #3 $148.86   12.363%   $167.2636   $167.26   $167.25   $167.30  
  Purchase #4 $166.72   8.454%   $180.8145   $180.81   $180.80   $180.80  
  Purchase #5 $130.95   7.621%   $140.9297   $140.93   $140.95   $140.90  
  Purchase #6 $241.73   7.769%   $260.51   $260.51   $260.50   $260.50  
  Purchase #7 $175.68   11.858%   $196.5121   $196.51   $196.50   $196.50  
  7 purchase totals = $1,165.63       $1,274.9447   $1,274.93   $1,274.90   $1,275.00