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 $165.71   8.790%   $180.2759   $180.28   $180.30   $180.30  
  Purchase #2 $233.81   13.438%   $265.2294   $265.23   $265.25   $265.20  
  Purchase #3 $216.73   9.184%   $236.6345   $236.63   $236.65   $236.60  
  Purchase #4 $87.68   9.444%   $95.9605   $95.96   $95.95   $96.00  
  Purchase #5 $97.38   8.767%   $105.9173   $105.92   $105.90   $105.90  
  Purchase #6 $191.87   3.479%   $198.5452   $198.55   $198.55   $198.50  
  Purchase #7 $76.48   9.185%   $83.5047   $83.50   $83.50   $83.50  
  7 purchase totals = $1,069.66       $1,166.0675   $1,166.07   $1,166.10   $1,166.00