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 $61.59   3.693%   $63.8645   $63.86   $63.85   $63.90  
  Purchase #2 $94.86   10.219%   $104.5537   $104.55   $104.55   $104.60  
  Purchase #3 $95.34   12.547%   $107.3023   $107.30   $107.30   $107.30  
  Purchase #4 $97.89   11.181%   $108.8351   $108.84   $108.85   $108.80  
  Purchase #5 $37.25   7.856%   $40.1764   $40.18   $40.20   $40.20  
  Purchase #6 $238.94   5.719%   $252.605   $252.61   $252.60   $252.60  
  Purchase #7 $99.91   3.778%   $103.6846   $103.68   $103.70   $103.70  
  7 purchase totals = $725.78       $781.0216   $781.02   $781.05   $781.10