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 $64.29   6.834%   $68.6836   $68.68   $68.70   $68.70  
  Purchase #2 $103.65   9.494%   $113.4905   $113.49   $113.50   $113.50  
  Purchase #3 $199.30   4.557%   $208.3821   $208.38   $208.40   $208.40  
  Purchase #4 $119.26   13.585%   $135.4615   $135.46   $135.45   $135.50  
  Purchase #5 $240.41   13.274%   $272.322   $272.32   $272.30   $272.30  
  Purchase #6 $183.40   11.289%   $204.104   $204.10   $204.10   $204.10  
  Purchase #7 $243.49   7.499%   $261.7493   $261.75   $261.75   $261.70  
  7 purchase totals = $1,153.80       $1,264.1930   $1,264.18   $1,264.20   $1,264.20