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 $139.74   10.114%   $153.8733   $153.87   $153.85   $153.90  
  Purchase #2 $198.68   6.723%   $212.0373   $212.04   $212.05   $212.00  
  Purchase #3 $171.74   13.488%   $194.9043   $194.90   $194.90   $194.90  
  Purchase #4 $46.72   8.360%   $50.6258   $50.63   $50.65   $50.60  
  Purchase #5 $87.99   5.617%   $92.9324   $92.93   $92.95   $92.90  
  Purchase #6 $225.77   6.135%   $239.621   $239.62   $239.60   $239.60  
  Purchase #7 $93.82   6.167%   $99.6059   $99.61   $99.60   $99.60  
  7 purchase totals = $964.46       $1,043.6000   $1,043.60   $1,043.60   $1,043.50