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 $241.87   13.656%   $274.8998   $274.90   $274.90   $274.90  
  Purchase #2 $231.42   4.263%   $241.2854   $241.29   $241.30   $241.30  
  Purchase #3 $44.56   4.139%   $46.4043   $46.40   $46.40   $46.40  
  Purchase #4 $119.84   10.258%   $132.1332   $132.13   $132.15   $132.10  
  Purchase #5 $225.58   6.117%   $239.3787   $239.38   $239.40   $239.40  
  Purchase #6 $200.85   10.377%   $221.6922   $221.69   $221.70   $221.70  
  Purchase #7 $43.64   12.394%   $49.0487   $49.05   $49.05   $49.00  
  7 purchase totals = $1,107.76       $1,204.8423   $1,204.84   $1,204.90   $1,204.80