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 $60.82   11.260%   $67.6683   $67.67   $67.65   $67.70  
  Purchase #2 $244.75   9.730%   $268.5642   $268.56   $268.55   $268.60  
  Purchase #3 $224.97   13.711%   $255.8156   $255.82   $255.80   $255.80  
  Purchase #4 $125.93   9.329%   $137.678   $137.68   $137.70   $137.70  
  Purchase #5 $6.71   9.387%   $7.3399   $7.34   $7.35   $7.30  
  Purchase #6 $106.84   4.874%   $112.0474   $112.05   $112.05   $112.00  
  Purchase #7 $140.55   7.724%   $151.4061   $151.41   $151.40   $151.40  
  7 purchase totals = $910.57       $1,000.5195   $1,000.53   $1,000.50   $1,000.50