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 $89.38   6.784%   $95.4435   $95.44   $95.45   $95.40  
  Purchase #2 $14.93   6.642%   $15.9217   $15.92   $15.90   $15.90  
  Purchase #3 $68.37   4.118%   $71.1855   $71.19   $71.20   $71.20  
  Purchase #4 $233.63   6.783%   $249.4771   $249.48   $249.50   $249.50  
  Purchase #5 $135.79   6.806%   $145.0319   $145.03   $145.05   $145.00  
  Purchase #6 $217.77   4.679%   $227.9595   $227.96   $227.95   $228.00  
  Purchase #7 $187.86   9.697%   $206.0768   $206.08   $206.10   $206.10  
  7 purchase totals = $947.73       $1,011.0960   $1,011.10   $1,011.15   $1,011.10