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 $179.75   8.506%   $195.0395   $195.04   $195.05   $195.00  
  Purchase #2 $195.48   3.719%   $202.7499   $202.75   $202.75   $202.70  
  Purchase #3 $248.47   11.381%   $276.7484   $276.75   $276.75   $276.70  
  Purchase #4 $102.51   11.338%   $114.1326   $114.13   $114.15   $114.10  
  Purchase #5 $25.40   12.511%   $28.5778   $28.58   $28.60   $28.60  
  Purchase #6 $213.74   10.507%   $236.1977   $236.20   $236.20   $236.20  
  Purchase #7 $16.64   4.567%   $17.3999   $17.40   $17.40   $17.40  
  7 purchase totals = $981.99       $1,070.8458   $1,070.85   $1,070.90   $1,070.70