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 $53.95   12.292%   $60.5815   $60.58   $60.60   $60.60  
  Purchase #2 $84.37   12.634%   $95.0293   $95.03   $95.05   $95.00  
  Purchase #3 $53.39   7.614%   $57.4551   $57.46   $57.45   $57.50  
  Purchase #4 $87.30   11.366%   $97.2225   $97.22   $97.20   $97.20  
  Purchase #5 $130.55   9.839%   $143.3948   $143.39   $143.40   $143.40  
  Purchase #6 $8.79   6.728%   $9.3814   $9.38   $9.40   $9.40  
  Purchase #7 $240.47   7.793%   $259.2098   $259.21   $259.20   $259.20  
  7 purchase totals = $658.82       $722.2744   $722.27   $722.30   $722.30