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 $180.71   12.222%   $202.7964   $202.80   $202.80   $202.80  
  Purchase #2 $199.63   8.851%   $217.2993   $217.30   $217.30   $217.30  
  Purchase #3 $96.49   4.869%   $101.1881   $101.19   $101.20   $101.20  
  Purchase #4 $64.41   4.657%   $67.4096   $67.41   $67.40   $67.40  
  Purchase #5 $133.43   5.200%   $140.3684   $140.37   $140.35   $140.40  
  Purchase #6 $168.89   9.258%   $184.5258   $184.53   $184.55   $184.50  
  Purchase #7 $153.44   8.129%   $165.9131   $165.91   $165.90   $165.90  
  7 purchase totals = $997.00       $1,079.5007   $1,079.51   $1,079.50   $1,079.50