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 $109.51   5.660%   $115.7083   $115.71   $115.70   $115.70  
  Purchase #2 $205.40   9.111%   $224.114   $224.11   $224.10   $224.10  
  Purchase #3 $32.94   3.292%   $34.0244   $34.02   $34.00   $34.00  
  Purchase #4 $164.81   12.424%   $185.286   $185.29   $185.30   $185.30  
  Purchase #5 $193.80   4.871%   $203.24   $203.24   $203.25   $203.20  
  Purchase #6 $238.86   9.193%   $260.8184   $260.82   $260.80   $260.80  
  Purchase #7 $225.61   5.177%   $237.2898   $237.29   $237.30   $237.30  
  7 purchase totals = $1,170.93       $1,260.4809   $1,260.48   $1,260.45   $1,260.40