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 $106.55   10.533%   $117.7729   $117.77   $117.75   $117.80  
  Purchase #2 $168.70   13.590%   $191.6263   $191.63   $191.65   $191.60  
  Purchase #3 $77.48   5.194%   $81.5043   $81.50   $81.50   $81.50  
  Purchase #4 $22.53   9.792%   $24.7361   $24.74   $24.75   $24.70  
  Purchase #5 $26.31   11.153%   $29.2444   $29.24   $29.25   $29.20  
  Purchase #6 $214.54   12.542%   $241.4476   $241.45   $241.45   $241.40  
  Purchase #7 $36.64   12.862%   $41.3526   $41.35   $41.35   $41.40  
  7 purchase totals = $652.75       $727.6842   $727.68   $727.70   $727.60