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 $34.71   6.591%   $36.9977   $37.00   $37.00   $37.00  
  Purchase #2 $237.47   7.791%   $255.9713   $255.97   $255.95   $256.00  
  Purchase #3 $95.29   10.471%   $105.2678   $105.27   $105.25   $105.30  
  Purchase #4 $250.66   10.707%   $277.4982   $277.50   $277.50   $277.50  
  Purchase #5 $115.92   3.251%   $119.6886   $119.69   $119.70   $119.70  
  Purchase #6 $102.86   8.214%   $111.3089   $111.31   $111.30   $111.30  
  Purchase #7 $248.26   6.314%   $263.9351   $263.94   $263.95   $263.90  
  7 purchase totals = $1,085.17       $1,170.6676   $1,170.68   $1,170.65   $1,170.70