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 $234.36   6.299%   $249.1223   $249.12   $249.10   $249.10  
  Purchase #2 $87.94   12.232%   $98.6968   $98.70   $98.70   $98.70  
  Purchase #3 $123.64   8.294%   $133.8947   $133.89   $133.90   $133.90  
  Purchase #4 $157.32   11.382%   $175.2262   $175.23   $175.25   $175.20  
  Purchase #5 $192.53   6.639%   $205.3121   $205.31   $205.30   $205.30  
  Purchase #6 $216.92   12.813%   $244.714   $244.71   $244.70   $244.70  
  Purchase #7 $133.40   10.204%   $147.0121   $147.01   $147.00   $147.00  
  7 purchase totals = $1,146.11       $1,253.9782   $1,253.97   $1,253.95   $1,253.90