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 $226.84   9.421%   $248.2106   $248.21   $248.20   $248.20  
  Purchase #2 $62.82   11.497%   $70.0424   $70.04   $70.05   $70.00  
  Purchase #3 $6.43   8.699%   $6.9893   $6.99   $7.00   $7.00  
  Purchase #4 $117.86   10.730%   $130.5064   $130.51   $130.50   $130.50  
  Purchase #5 $176.84   13.606%   $200.9009   $200.90   $200.90   $200.90  
  Purchase #6 $60.94   8.305%   $66.0011   $66.00   $66.00   $66.00  
  Purchase #7 $84.35   8.519%   $91.5358   $91.54   $91.55   $91.50  
  7 purchase totals = $736.08       $814.1865   $814.19   $814.20   $814.10