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 $227.76   9.658%   $249.7571   $249.76   $249.75   $249.80  
  Purchase #2 $43.36   9.797%   $47.608   $47.61   $47.60   $47.60  
  Purchase #3 $31.73   9.339%   $34.6933   $34.69   $34.70   $34.70  
  Purchase #4 $244.90   11.713%   $273.5851   $273.59   $273.60   $273.60  
  Purchase #5 $14.31   4.787%   $14.995   $15.00   $15.00   $15.00  
  Purchase #6 $133.93   10.172%   $147.5534   $147.55   $147.55   $147.60  
  Purchase #7 $245.67   6.837%   $262.4665   $262.47   $262.45   $262.50  
  7 purchase totals = $941.66       $1,030.6584   $1,030.67   $1,030.65   $1,030.80