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 $186.48   8.187%   $201.7471   $201.75   $201.75   $201.70  
  Purchase #2 $152.54   9.661%   $167.2769   $167.28   $167.30   $167.30  
  Purchase #3 $227.35   6.554%   $242.2505   $242.25   $242.25   $242.30  
  Purchase #4 $154.87   11.596%   $172.8287   $172.83   $172.85   $172.80  
  Purchase #5 $9.27   10.351%   $10.2295   $10.23   $10.25   $10.20  
  Purchase #6 $75.25   8.221%   $81.4363   $81.44   $81.45   $81.40  
  Purchase #7 $79.29   4.193%   $82.6146   $82.61   $82.60   $82.60  
  7 purchase totals = $885.05       $958.3836   $958.39   $958.45   $958.30