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 $63.42   6.146%   $67.3178   $67.32   $67.30   $67.30  
  Purchase #2 $208.81   5.569%   $220.4386   $220.44   $220.45   $220.40  
  Purchase #3 $28.50   3.478%   $29.4912   $29.49   $29.50   $29.50  
  Purchase #4 $29.43   9.685%   $32.2803   $32.28   $32.30   $32.30  
  Purchase #5 $13.79   3.184%   $14.2291   $14.23   $14.25   $14.20  
  Purchase #6 $88.68   4.359%   $92.5456   $92.55   $92.55   $92.50  
  Purchase #7 $239.81   11.838%   $268.1987   $268.20   $268.20   $268.20  
  7 purchase totals = $672.44       $724.5013   $724.51   $724.55   $724.40