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 $93.43   3.462%   $96.6645   $96.66   $96.65   $96.70  
  Purchase #2 $182.45   4.845%   $191.2897   $191.29   $191.30   $191.30  
  Purchase #3 $179.80   10.826%   $199.2651   $199.27   $199.25   $199.30  
  Purchase #4 $19.99   8.725%   $21.7341   $21.73   $21.75   $21.70  
  Purchase #5 $239.87   7.422%   $257.6732   $257.67   $257.65   $257.70  
  Purchase #6 $211.62   10.157%   $233.1142   $233.11   $233.10   $233.10  
  Purchase #7 $12.99   12.242%   $14.5802   $14.58   $14.60   $14.60  
  7 purchase totals = $940.15       $1,014.3210   $1,014.31   $1,014.30   $1,014.40