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 $226.83   6.545%   $241.676   $241.68   $241.70   $241.70  
  Purchase #2 $39.73   13.359%   $45.0375   $45.04   $45.05   $45.00  
  Purchase #3 $41.99   4.856%   $44.029   $44.03   $44.05   $44.00  
  Purchase #4 $164.91   4.304%   $172.0077   $172.01   $172.00   $172.00  
  Purchase #5 $126.87   10.832%   $140.6126   $140.61   $140.60   $140.60  
  Purchase #6 $72.58   4.734%   $76.0159   $76.02   $76.00   $76.00  
  Purchase #7 $57.51   12.743%   $64.8385   $64.84   $64.85   $64.80  
  7 purchase totals = $730.42       $784.2172   $784.23   $784.25   $784.10