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 $194.39   6.496%   $207.0176   $207.02   $207.00   $207.00  
  Purchase #2 $131.75   12.447%   $148.1489   $148.15   $148.15   $148.10  
  Purchase #3 $240.44   11.157%   $267.2659   $267.27   $267.25   $267.30  
  Purchase #4 $204.26   5.799%   $216.105   $216.11   $216.10   $216.10  
  Purchase #5 $48.68   6.219%   $51.7074   $51.71   $51.70   $51.70  
  Purchase #6 $198.54   3.862%   $206.2076   $206.21   $206.20   $206.20  
  Purchase #7 $123.58   4.365%   $128.9743   $128.97   $128.95   $129.00  
  7 purchase totals = $1,141.64       $1,225.4267   $1,225.44   $1,225.35   $1,225.40