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 $194.66   8.802%   $211.794   $211.79   $211.80   $211.80  
  Purchase #2 $97.51   6.427%   $103.777   $103.78   $103.80   $103.80  
  Purchase #3 $226.62   4.427%   $236.6525   $236.65   $236.65   $236.70  
  Purchase #4 $138.67   9.565%   $151.9338   $151.93   $151.95   $151.90  
  Purchase #5 $249.43   12.454%   $280.494   $280.49   $280.50   $280.50  
  Purchase #6 $191.55   7.632%   $206.1691   $206.17   $206.15   $206.20  
  Purchase #7 $143.99   7.712%   $155.0945   $155.09   $155.10   $155.10  
  7 purchase totals = $1,242.43       $1,345.9149   $1,345.90   $1,345.95   $1,346.00