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 $40.82   13.207%   $46.2111   $46.21   $46.20   $46.20  
  Purchase #2 $244.88   12.751%   $276.1046   $276.10   $276.10   $276.10  
  Purchase #3 $238.35   8.491%   $258.5883   $258.59   $258.60   $258.60  
  Purchase #4 $12.82   12.326%   $14.4002   $14.40   $14.40   $14.40  
  Purchase #5 $249.42   8.730%   $271.1944   $271.19   $271.20   $271.20  
  Purchase #6 $101.42   11.478%   $113.061   $113.06   $113.05   $113.10  
  Purchase #7 $173.71   5.474%   $183.2189   $183.22   $183.20   $183.20  
  7 purchase totals = $1,061.42       $1,162.7785   $1,162.77   $1,162.75   $1,162.80