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 $221.61   5.111%   $232.9365   $232.94   $232.95   $232.90  
  Purchase #2 $161.28   10.787%   $178.6773   $178.68   $178.70   $178.70  
  Purchase #3 $95.33   9.803%   $104.6752   $104.68   $104.70   $104.70  
  Purchase #4 $203.30   4.862%   $213.1844   $213.18   $213.20   $213.20  
  Purchase #5 $239.78   10.606%   $265.2111   $265.21   $265.20   $265.20  
  Purchase #6 $209.64   5.569%   $221.3149   $221.31   $221.30   $221.30  
  Purchase #7 $225.26   8.241%   $243.8237   $243.82   $243.80   $243.80  
  7 purchase totals = $1,356.20       $1,459.8231   $1,459.82   $1,459.85   $1,459.80