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 $56.41   8.112%   $60.986   $60.99   $61.00   $61.00  
  Purchase #2 $112.62   5.109%   $118.3738   $118.37   $118.35   $118.40  
  Purchase #3 $140.37   13.442%   $159.2385   $159.24   $159.25   $159.20  
  Purchase #4 $190.68   5.572%   $201.3047   $201.30   $201.30   $201.30  
  Purchase #5 $144.53   5.443%   $152.3968   $152.40   $152.40   $152.40  
  Purchase #6 $125.93   8.416%   $136.5283   $136.53   $136.55   $136.50  
  Purchase #7 $173.88   12.749%   $196.048   $196.05   $196.05   $196.00  
  7 purchase totals = $944.42       $1,024.8761   $1,024.88   $1,024.90   $1,024.80