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 $204.99   9.349%   $224.1545   $224.15   $224.15   $224.20  
  Purchase #2 $72.60   8.699%   $78.9155   $78.92   $78.90   $78.90  
  Purchase #3 $169.77   11.771%   $189.7536   $189.75   $189.75   $189.80  
  Purchase #4 $66.96   3.756%   $69.475   $69.48   $69.50   $69.50  
  Purchase #5 $153.27   13.603%   $174.1193   $174.12   $174.10   $174.10  
  Purchase #6 $172.62   10.247%   $190.3084   $190.31   $190.30   $190.30  
  Purchase #7 $70.27   6.379%   $74.7525   $74.75   $74.75   $74.80  
  7 purchase totals = $910.48       $1,001.4788   $1,001.48   $1,001.45   $1,001.60