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 $51.28   13.570%   $58.2387   $58.24   $58.25   $58.20  
  Purchase #2 $115.55   11.427%   $128.7539   $128.75   $128.75   $128.80  
  Purchase #3 $247.64   12.485%   $278.5579   $278.56   $278.55   $278.60  
  Purchase #4 $68.86   8.388%   $74.636   $74.64   $74.65   $74.60  
  Purchase #5 $225.45   5.828%   $238.5892   $238.59   $238.60   $238.60  
  Purchase #6 $248.31   11.355%   $276.5056   $276.51   $276.50   $276.50  
  Purchase #7 $224.98   6.420%   $239.4237   $239.42   $239.40   $239.40  
  7 purchase totals = $1,182.07       $1,294.7050   $1,294.71   $1,294.70   $1,294.70