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 $68.97   3.122%   $71.1232   $71.12   $71.10   $71.10  
  Purchase #2 $175.60   11.749%   $196.2312   $196.23   $196.25   $196.20  
  Purchase #3 $77.37   8.653%   $84.0648   $84.06   $84.05   $84.10  
  Purchase #4 $119.70   7.174%   $128.2873   $128.29   $128.30   $128.30  
  Purchase #5 $52.75   13.755%   $60.0058   $60.01   $60.00   $60.00  
  Purchase #6 $250.29   7.286%   $268.5261   $268.53   $268.55   $268.50  
  Purchase #7 $33.26   10.120%   $36.6259   $36.63   $36.65   $36.60  
  7 purchase totals = $777.94       $844.8643   $844.87   $844.90   $844.80