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 $82.28   12.551%   $92.607   $92.61   $92.60   $92.60  
  Purchase #2 $179.31   3.367%   $185.3474   $185.35   $185.35   $185.30  
  Purchase #3 $187.34   6.477%   $199.474   $199.47   $199.45   $199.50  
  Purchase #4 $75.39   8.316%   $81.6594   $81.66   $81.65   $81.70  
  Purchase #5 $52.80   9.486%   $57.8086   $57.81   $57.80   $57.80  
  Purchase #6 $195.75   13.110%   $221.4128   $221.41   $221.40   $221.40  
  Purchase #7 $21.56   12.532%   $24.2619   $24.26   $24.25   $24.30  
  7 purchase totals = $794.43       $862.5711   $862.57   $862.50   $862.60