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 $247.67   8.617%   $269.0117   $269.01   $269.00   $269.00  
  Purchase #2 $132.53   7.687%   $142.7176   $142.72   $142.70   $142.70  
  Purchase #3 $27.44   11.427%   $30.5756   $30.58   $30.60   $30.60  
  Purchase #4 $185.74   7.185%   $199.0854   $199.09   $199.10   $199.10  
  Purchase #5 $135.32   11.718%   $151.1768   $151.18   $151.20   $151.20  
  Purchase #6 $92.45   12.629%   $104.1255   $104.13   $104.15   $104.10  
  Purchase #7 $100.75   11.176%   $112.0098   $112.01   $112.00   $112.00  
  7 purchase totals = $921.90       $1,008.7024   $1,008.72   $1,008.75   $1,008.70