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 $227.61   6.179%   $241.674   $241.67   $241.65   $241.70  
  Purchase #2 $219.65   11.214%   $244.2816   $244.28   $244.30   $244.30  
  Purchase #3 $196.97   9.362%   $215.4103   $215.41   $215.40   $215.40  
  Purchase #4 $47.71   10.313%   $52.6303   $52.63   $52.65   $52.60  
  Purchase #5 $109.36   8.435%   $118.5845   $118.58   $118.60   $118.60  
  Purchase #6 $33.51   8.824%   $36.4669   $36.47   $36.45   $36.50  
  Purchase #7 $209.95   11.579%   $234.2601   $234.26   $234.25   $234.30  
  7 purchase totals = $1,044.76       $1,143.3077   $1,143.30   $1,143.30   $1,143.40