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 $119.29   5.267%   $125.573   $125.57   $125.55   $125.60  
  Purchase #2 $37.39   11.173%   $41.5676   $41.57   $41.55   $41.60  
  Purchase #3 $187.34   5.763%   $198.1364   $198.14   $198.15   $198.10  
  Purchase #4 $221.81   13.714%   $252.229   $252.23   $252.25   $252.20  
  Purchase #5 $92.70   12.461%   $104.2513   $104.25   $104.25   $104.30  
  Purchase #6 $79.44   7.518%   $85.4123   $85.41   $85.40   $85.40  
  Purchase #7 $22.49   12.662%   $25.3377   $25.34   $25.35   $25.30  
  7 purchase totals = $760.46       $832.5073   $832.51   $832.50   $832.50