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 $244.69   13.214%   $277.0233   $277.02   $277.00   $277.00  
  Purchase #2 $223.51   4.348%   $233.2282   $233.23   $233.25   $233.20  
  Purchase #3 $119.73   12.465%   $134.6543   $134.65   $134.65   $134.70  
  Purchase #4 $129.47   11.238%   $144.0198   $144.02   $144.00   $144.00  
  Purchase #5 $215.57   13.432%   $244.5254   $244.53   $244.55   $244.50  
  Purchase #6 $244.31   6.187%   $259.4255   $259.43   $259.45   $259.40  
  Purchase #7 $8.72   8.379%   $9.4506   $9.45   $9.45   $9.50  
  7 purchase totals = $1,186.00       $1,302.3271   $1,302.33   $1,302.35   $1,302.30