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 $228.30   8.393%   $247.4612   $247.46   $247.45   $247.50  
  Purchase #2 $153.63   8.610%   $166.8575   $166.86   $166.85   $166.90  
  Purchase #3 $200.99   6.439%   $213.9317   $213.93   $213.95   $213.90  
  Purchase #4 $233.66   6.386%   $248.5815   $248.58   $248.60   $248.60  
  Purchase #5 $89.67   9.302%   $98.0111   $98.01   $98.00   $98.00  
  Purchase #6 $225.91   13.592%   $256.6157   $256.62   $256.60   $256.60  
  Purchase #7 $235.41   6.838%   $251.5073   $251.51   $251.50   $251.50  
  7 purchase totals = $1,367.57       $1,482.9660   $1,482.97   $1,482.95   $1,483.00