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 $12.82   4.750%   $13.429   $13.43   $13.45   $13.40  
  Purchase #2 $110.60   10.198%   $121.879   $121.88   $121.90   $121.90  
  Purchase #3 $56.28   10.759%   $62.3352   $62.34   $62.35   $62.30  
  Purchase #4 $176.66   12.296%   $198.3821   $198.38   $198.40   $198.40  
  Purchase #5 $12.97   5.495%   $13.6827   $13.68   $13.70   $13.70  
  Purchase #6 $16.78   8.663%   $18.2337   $18.23   $18.25   $18.20  
  Purchase #7 $11.57   7.138%   $12.3959   $12.40   $12.40   $12.40  
  7 purchase totals = $397.68       $440.3376   $440.34   $440.45   $440.30