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 $92.73   11.704%   $103.5831   $103.58   $103.60   $103.60  
  Purchase #2 $232.93   12.463%   $261.9601   $261.96   $261.95   $262.00  
  Purchase #3 $16.79   4.416%   $17.5314   $17.53   $17.55   $17.50  
  Purchase #4 $237.85   3.151%   $245.3447   $245.34   $245.35   $245.30  
  Purchase #5 $31.99   7.651%   $34.4376   $34.44   $34.45   $34.40  
  Purchase #6 $237.75   7.274%   $255.0439   $255.04   $255.05   $255.00  
  Purchase #7 $205.77   13.139%   $232.8061   $232.81   $232.80   $232.80  
  7 purchase totals = $1,055.81       $1,150.7069   $1,150.70   $1,150.75   $1,150.60