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 $134.56   6.670%   $143.5352   $143.54   $143.55   $143.50  
  Purchase #2 $192.45   13.146%   $217.7495   $217.75   $217.75   $217.70  
  Purchase #3 $112.76   10.465%   $124.5603   $124.56   $124.55   $124.60  
  Purchase #4 $203.78   6.545%   $217.1174   $217.12   $217.10   $217.10  
  Purchase #5 $211.71   7.207%   $226.9679   $226.97   $226.95   $227.00  
  Purchase #6 $47.75   6.599%   $50.901   $50.90   $50.90   $50.90  
  Purchase #7 $37.65   12.644%   $42.4105   $42.41   $42.40   $42.40  
  7 purchase totals = $940.66       $1,023.2418   $1,023.25   $1,023.20   $1,023.20