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 $112.75   12.303%   $126.6216   $126.62   $126.60   $126.60  
  Purchase #2 $162.41   9.421%   $177.7106   $177.71   $177.70   $177.70  
  Purchase #3 $203.80   10.104%   $224.392   $224.39   $224.40   $224.40  
  Purchase #4 $137.59   10.682%   $152.2874   $152.29   $152.30   $152.30  
  Purchase #5 $38.55   11.107%   $42.8317   $42.83   $42.85   $42.80  
  Purchase #6 $118.29   10.535%   $130.7519   $130.75   $130.75   $130.80  
  Purchase #7 $15.35   6.602%   $16.3634   $16.36   $16.35   $16.40  
  7 purchase totals = $788.74       $870.9586   $870.95   $870.95   $871.00