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 $216.68   13.302%   $245.5028   $245.50   $245.50   $245.50  
  Purchase #2 $205.62   6.439%   $218.8599   $218.86   $218.85   $218.90  
  Purchase #3 $168.98   3.460%   $174.8267   $174.83   $174.85   $174.80  
  Purchase #4 $249.59   7.623%   $268.6162   $268.62   $268.60   $268.60  
  Purchase #5 $208.67   10.668%   $230.9309   $230.93   $230.95   $230.90  
  Purchase #6 $12.92   4.458%   $13.496   $13.50   $13.50   $13.50  
  Purchase #7 $6.42   6.371%   $6.829   $6.83   $6.85   $6.80  
  7 purchase totals = $1,068.88       $1,159.0615   $1,159.07   $1,159.10   $1,159.00