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 $55.44   11.717%   $61.9359   $61.94   $61.95   $61.90  
  Purchase #2 $102.59   10.690%   $113.5569   $113.56   $113.55   $113.60  
  Purchase #3 $6.42   5.226%   $6.7555   $6.76   $6.75   $6.80  
  Purchase #4 $27.49   10.472%   $30.3688   $30.37   $30.35   $30.40  
  Purchase #5 $248.31   11.574%   $277.0494   $277.05   $277.05   $277.00  
  Purchase #6 $221.67   8.285%   $240.0354   $240.04   $240.05   $240.00  
  Purchase #7 $230.53   10.836%   $255.5102   $255.51   $255.50   $255.50  
  7 purchase totals = $892.45       $985.2121   $985.23   $985.20   $985.20