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 $168.53   13.623%   $191.4888   $191.49   $191.50   $191.50  
  Purchase #2 $220.55   5.458%   $232.5876   $232.59   $232.60   $232.60  
  Purchase #3 $60.30   8.520%   $65.4376   $65.44   $65.45   $65.40  
  Purchase #4 $206.87   3.326%   $213.7505   $213.75   $213.75   $213.80  
  Purchase #5 $164.70   13.688%   $187.2441   $187.24   $187.25   $187.20  
  Purchase #6 $195.45   10.429%   $215.8335   $215.83   $215.85   $215.80  
  Purchase #7 $49.86   5.813%   $52.7584   $52.76   $52.75   $52.80  
  7 purchase totals = $1,066.26       $1,159.1005   $1,159.10   $1,159.15   $1,159.10