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 $172.71   8.124%   $186.741   $186.74   $186.75   $186.70  
  Purchase #2 $76.54   10.223%   $84.3647   $84.36   $84.35   $84.40  
  Purchase #3 $112.47   3.683%   $116.6123   $116.61   $116.60   $116.60  
  Purchase #4 $137.60   11.172%   $152.9727   $152.97   $152.95   $153.00  
  Purchase #5 $163.68   11.706%   $182.8404   $182.84   $182.85   $182.80  
  Purchase #6 $159.26   9.530%   $174.4375   $174.44   $174.45   $174.40  
  Purchase #7 $97.28   6.245%   $103.3551   $103.36   $103.35   $103.40  
  7 purchase totals = $919.54       $1,001.3237   $1,001.32   $1,001.30   $1,001.30