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 $119.85   11.214%   $133.29   $133.29   $133.30   $133.30  
  Purchase #2 $194.72   11.617%   $217.3406   $217.34   $217.35   $217.30  
  Purchase #3 $151.79   10.539%   $167.7871   $167.79   $167.80   $167.80  
  Purchase #4 $222.81   8.811%   $242.4418   $242.44   $242.45   $242.40  
  Purchase #5 $150.75   10.554%   $166.6602   $166.66   $166.65   $166.70  
  Purchase #6 $173.55   10.564%   $191.8838   $191.88   $191.90   $191.90  
  Purchase #7 $204.50   3.605%   $211.8722   $211.87   $211.85   $211.90  
  7 purchase totals = $1,217.97       $1,331.2757   $1,331.27   $1,331.30   $1,331.30