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 $48.47   8.862%   $52.7654   $52.77   $52.75   $52.80  
  Purchase #2 $195.54   11.756%   $218.5277   $218.53   $218.55   $218.50  
  Purchase #3 $233.91   9.870%   $256.9969   $257.00   $257.00   $257.00  
  Purchase #4 $70.30   7.515%   $75.583   $75.58   $75.60   $75.60  
  Purchase #5 $12.98   9.304%   $14.1877   $14.19   $14.20   $14.20  
  Purchase #6 $56.44   5.136%   $59.3388   $59.34   $59.35   $59.30  
  Purchase #7 $81.89   6.132%   $86.9115   $86.91   $86.90   $86.90  
  7 purchase totals = $699.53       $764.3110   $764.32   $764.35   $764.30