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 $245.65   12.246%   $275.7323   $275.73   $275.75   $275.70  
  Purchase #2 $177.99   13.714%   $202.3995   $202.40   $202.40   $202.40  
  Purchase #3 $151.51   6.214%   $160.9248   $160.92   $160.90   $160.90  
  Purchase #4 $117.81   11.436%   $131.2828   $131.28   $131.30   $131.30  
  Purchase #5 $15.56   6.233%   $16.5299   $16.53   $16.55   $16.50  
  Purchase #6 $31.53   11.460%   $35.1433   $35.14   $35.15   $35.10  
  Purchase #7 $218.29   12.424%   $245.4103   $245.41   $245.40   $245.40  
  7 purchase totals = $958.34       $1,067.4229   $1,067.41   $1,067.45   $1,067.30