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 $233.78   8.854%   $254.4789   $254.48   $254.50   $254.50  
  Purchase #2 $246.66   8.428%   $267.4485   $267.45   $267.45   $267.40  
  Purchase #3 $62.34   11.264%   $69.362   $69.36   $69.35   $69.40  
  Purchase #4 $186.38   7.154%   $199.7136   $199.71   $199.70   $199.70  
  Purchase #5 $114.49   3.591%   $118.6013   $118.60   $118.60   $118.60  
  Purchase #6 $123.39   11.267%   $137.2924   $137.29   $137.30   $137.30  
  Purchase #7 $169.95   11.627%   $189.7101   $189.71   $189.70   $189.70  
  7 purchase totals = $1,136.99       $1,236.6068   $1,236.60   $1,236.60   $1,236.60