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 $49.76   5.823%   $52.6575   $52.66   $52.65   $52.70  
  Purchase #2 $176.47   10.679%   $195.3152   $195.32   $195.30   $195.30  
  Purchase #3 $87.46   7.151%   $93.7143   $93.71   $93.70   $93.70  
  Purchase #4 $187.48   13.589%   $212.9567   $212.96   $212.95   $213.00  
  Purchase #5 $249.38   12.656%   $280.9415   $280.94   $280.95   $280.90  
  Purchase #6 $241.61   9.149%   $263.7149   $263.71   $263.70   $263.70  
  Purchase #7 $201.57   6.189%   $214.0452   $214.05   $214.05   $214.00  
  7 purchase totals = $1,193.73       $1,313.3453   $1,313.35   $1,313.30   $1,313.30