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 $82.55   4.118%   $85.9494   $85.95   $85.95   $85.90  
  Purchase #2 $145.82   7.782%   $157.1677   $157.17   $157.15   $157.20  
  Purchase #3 $212.78   4.182%   $221.6785   $221.68   $221.70   $221.70  
  Purchase #4 $24.35   8.544%   $26.4305   $26.43   $26.45   $26.40  
  Purchase #5 $94.87   13.706%   $107.8729   $107.87   $107.85   $107.90  
  Purchase #6 $97.55   11.686%   $108.9497   $108.95   $108.95   $108.90  
  Purchase #7 $117.80   10.607%   $130.295   $130.30   $130.30   $130.30  
  7 purchase totals = $775.72       $838.3437   $838.35   $838.35   $838.30