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 $188.25   4.607%   $196.9227   $196.92   $196.90   $196.90  
  Purchase #2 $114.87   12.624%   $129.3712   $129.37   $129.35   $129.40  
  Purchase #3 $76.61   10.422%   $84.5943   $84.59   $84.60   $84.60  
  Purchase #4 $226.96   6.374%   $241.4264   $241.43   $241.45   $241.40  
  Purchase #5 $155.50   6.447%   $165.5251   $165.53   $165.55   $165.50  
  Purchase #6 $26.77   4.800%   $28.055   $28.06   $28.05   $28.10  
  Purchase #7 $70.99   13.577%   $80.6283   $80.63   $80.65   $80.60  
  7 purchase totals = $859.95       $926.5230   $926.53   $926.55   $926.50