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 $32.51   11.358%   $36.2025   $36.20   $36.20   $36.20  
  Purchase #2 $233.43   12.523%   $262.6624   $262.66   $262.65   $262.70  
  Purchase #3 $83.67   10.452%   $92.4152   $92.42   $92.40   $92.40  
  Purchase #4 $184.44   3.352%   $190.6224   $190.62   $190.60   $190.60  
  Purchase #5 $103.70   11.516%   $115.6421   $115.64   $115.65   $115.60  
  Purchase #6 $194.59   13.717%   $221.2819   $221.28   $221.30   $221.30  
  Purchase #7 $148.25   12.756%   $167.1608   $167.16   $167.15   $167.20  
  7 purchase totals = $980.59       $1,085.9873   $1,085.98   $1,085.95   $1,086.00