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 $163.30   12.540%   $183.7778   $183.78   $183.80   $183.80  
  Purchase #2 $167.46   3.767%   $173.7682   $173.77   $173.75   $173.80  
  Purchase #3 $7.60   3.485%   $7.8649   $7.86   $7.85   $7.90  
  Purchase #4 $163.85   4.662%   $171.4887   $171.49   $171.50   $171.50  
  Purchase #5 $20.74   11.812%   $23.1898   $23.19   $23.20   $23.20  
  Purchase #6 $227.59   6.471%   $242.3173   $242.32   $242.30   $242.30  
  Purchase #7 $89.82   11.297%   $99.967   $99.97   $99.95   $100.00  
  7 purchase totals = $840.36       $902.3737   $902.38   $902.35   $902.50