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 $107.53   8.125%   $116.2668   $116.27   $116.25   $116.30  
  Purchase #2 $197.76   7.164%   $211.9275   $211.93   $211.95   $211.90  
  Purchase #3 $250.64   8.224%   $271.2526   $271.25   $271.25   $271.30  
  Purchase #4 $94.47   10.584%   $104.4687   $104.47   $104.45   $104.50  
  Purchase #5 $250.95   3.183%   $258.9377   $258.94   $258.95   $258.90  
  Purchase #6 $178.29   11.516%   $198.8219   $198.82   $198.80   $198.80  
  Purchase #7 $5.83   12.211%   $6.5419   $6.54   $6.55   $6.50  
  7 purchase totals = $1,085.47       $1,168.2171   $1,168.22   $1,168.20   $1,168.20