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 $66.88   12.283%   $75.0949   $75.09   $75.10   $75.10  
  Purchase #2 $239.68   7.138%   $256.7884   $256.79   $256.80   $256.80  
  Purchase #3 $54.65   13.308%   $61.9228   $61.92   $61.90   $61.90  
  Purchase #4 $176.56   7.275%   $189.4047   $189.40   $189.40   $189.40  
  Purchase #5 $215.99   7.350%   $231.8653   $231.87   $231.85   $231.90  
  Purchase #6 $233.34   3.247%   $240.9165   $240.92   $240.90   $240.90  
  Purchase #7 $180.32   13.349%   $204.3909   $204.39   $204.40   $204.40  
  7 purchase totals = $1,167.42       $1,260.3835   $1,260.38   $1,260.35   $1,260.40