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 $113.51   4.498%   $118.6157   $118.62   $118.60   $118.60  
  Purchase #2 $224.91   11.489%   $250.7499   $250.75   $250.75   $250.70  
  Purchase #3 $59.93   12.781%   $67.5897   $67.59   $67.60   $67.60  
  Purchase #4 $56.67   3.359%   $58.5735   $58.57   $58.55   $58.60  
  Purchase #5 $140.62   5.514%   $148.3738   $148.37   $148.35   $148.40  
  Purchase #6 $49.41   8.776%   $53.7462   $53.75   $53.75   $53.70  
  Purchase #7 $111.63   6.782%   $119.2007   $119.20   $119.20   $119.20  
  7 purchase totals = $756.68       $816.8495   $816.85   $816.80   $816.80