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 $203.56   11.479%   $226.9267   $226.93   $226.95   $226.90  
  Purchase #2 $121.76   10.513%   $134.5606   $134.56   $134.55   $134.60  
  Purchase #3 $68.74   11.432%   $76.5984   $76.60   $76.60   $76.60  
  Purchase #4 $113.90   6.590%   $121.406   $121.41   $121.40   $121.40  
  Purchase #5 $249.97   5.157%   $262.861   $262.86   $262.85   $262.90  
  Purchase #6 $175.60   11.152%   $195.1829   $195.18   $195.20   $195.20  
  Purchase #7 $28.88   11.352%   $32.1585   $32.16   $32.15   $32.20  
  7 purchase totals = $962.41       $1,049.6941   $1,049.70   $1,049.70   $1,049.80