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 $45.40   5.223%   $47.7712   $47.77   $47.75   $47.80  
  Purchase #2 $183.71   11.862%   $205.5017   $205.50   $205.50   $205.50  
  Purchase #3 $105.51   7.713%   $113.648   $113.65   $113.65   $113.60  
  Purchase #4 $39.99   6.781%   $42.7017   $42.70   $42.70   $42.70  
  Purchase #5 $45.78   6.515%   $48.7626   $48.76   $48.75   $48.80  
  Purchase #6 $183.77   9.152%   $200.5886   $200.59   $200.60   $200.60  
  Purchase #7 $240.74   7.495%   $258.7835   $258.78   $258.80   $258.80  
  7 purchase totals = $844.90       $917.7573   $917.75   $917.75   $917.80