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 $153.62   13.591%   $174.4985   $174.50   $174.50   $174.50  
  Purchase #2 $225.82   10.557%   $249.6598   $249.66   $249.65   $249.70  
  Purchase #3 $219.72   12.814%   $247.8749   $247.87   $247.85   $247.90  
  Purchase #4 $73.63   12.476%   $82.8161   $82.82   $82.80   $82.80  
  Purchase #5 $116.81   11.511%   $130.256   $130.26   $130.25   $130.30  
  Purchase #6 $43.95   3.480%   $45.4795   $45.48   $45.50   $45.50  
  Purchase #7 $133.99   10.609%   $148.205   $148.21   $148.20   $148.20  
  7 purchase totals = $967.54       $1,078.7898   $1,078.80   $1,078.75   $1,078.90