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 $213.87   12.191%   $239.9429   $239.94   $239.95   $239.90  
  Purchase #2 $91.96   3.423%   $95.1078   $95.11   $95.10   $95.10  
  Purchase #3 $142.95   9.428%   $156.4273   $156.43   $156.45   $156.40  
  Purchase #4 $15.53   8.660%   $16.8749   $16.87   $16.85   $16.90  
  Purchase #5 $202.30   6.179%   $214.8001   $214.80   $214.80   $214.80  
  Purchase #6 $143.67   11.778%   $160.5915   $160.59   $160.60   $160.60  
  Purchase #7 $187.67   7.259%   $201.293   $201.29   $201.30   $201.30  
  7 purchase totals = $997.95       $1,085.0375   $1,085.03   $1,085.05   $1,085.00