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 $54.47   4.390%   $56.8612   $56.86   $56.85   $56.90  
  Purchase #2 $175.79   11.200%   $195.4785   $195.48   $195.50   $195.50  
  Purchase #3 $41.38   4.394%   $43.1982   $43.20   $43.20   $43.20  
  Purchase #4 $208.93   7.588%   $224.7836   $224.78   $224.80   $224.80  
  Purchase #5 $116.69   8.208%   $126.2679   $126.27   $126.25   $126.30  
  Purchase #6 $22.32   8.194%   $24.1489   $24.15   $24.15   $24.10  
  Purchase #7 $109.71   10.514%   $121.2449   $121.24   $121.25   $121.20  
  7 purchase totals = $729.29       $791.9832   $791.98   $792.00   $792.00