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 $227.56   11.834%   $254.4895   $254.49   $254.50   $254.50  
  Purchase #2 $185.70   10.374%   $204.9645   $204.96   $204.95   $205.00  
  Purchase #3 $102.44   4.819%   $107.3766   $107.38   $107.40   $107.40  
  Purchase #4 $94.68   4.436%   $98.88   $98.88   $98.90   $98.90  
  Purchase #5 $167.95   7.380%   $180.3447   $180.34   $180.35   $180.30  
  Purchase #6 $224.94   3.445%   $232.6892   $232.69   $232.70   $232.70  
  Purchase #7 $173.95   5.290%   $183.152   $183.15   $183.15   $183.20  
  7 purchase totals = $1,177.22       $1,261.8965   $1,261.89   $1,261.95   $1,262.00