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 $55.46   12.281%   $62.271   $62.27   $62.25   $62.30  
  Purchase #2 $187.40   9.845%   $205.8495   $205.85   $205.85   $205.80  
  Purchase #3 $76.36   6.699%   $81.4754   $81.48   $81.50   $81.50  
  Purchase #4 $32.31   5.306%   $34.0244   $34.02   $34.00   $34.00  
  Purchase #5 $245.66   8.565%   $266.7008   $266.70   $266.70   $266.70  
  Purchase #6 $210.91   9.385%   $230.7039   $230.70   $230.70   $230.70  
  Purchase #7 $92.69   3.691%   $96.1112   $96.11   $96.10   $96.10  
  7 purchase totals = $900.79       $977.1362   $977.13   $977.10   $977.10