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 $67.41   8.691%   $73.2686   $73.27   $73.25   $73.30  
  Purchase #2 $28.36   8.140%   $30.6685   $30.67   $30.65   $30.70  
  Purchase #3 $74.75   5.759%   $79.0549   $79.05   $79.05   $79.10  
  Purchase #4 $211.89   4.470%   $221.3615   $221.36   $221.35   $221.40  
  Purchase #5 $195.82   12.821%   $220.9261   $220.93   $220.95   $220.90  
  Purchase #6 $150.43   7.354%   $161.4926   $161.49   $161.50   $161.50  
  Purchase #7 $7.82   7.702%   $8.4223   $8.42   $8.40   $8.40  
  7 purchase totals = $736.48       $795.1945   $795.19   $795.15   $795.30