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 $144.77   10.697%   $160.256   $160.26   $160.25   $160.30  
  Purchase #2 $232.78   9.831%   $255.6646   $255.66   $255.65   $255.70  
  Purchase #3 $205.99   4.248%   $214.7405   $214.74   $214.75   $214.70  
  Purchase #4 $113.88   9.689%   $124.9138   $124.91   $124.90   $124.90  
  Purchase #5 $6.59   3.151%   $6.7977   $6.80   $6.80   $6.80  
  Purchase #6 $141.91   7.248%   $152.1956   $152.20   $152.20   $152.20  
  Purchase #7 $103.68   13.749%   $117.935   $117.94   $117.95   $117.90  
  7 purchase totals = $949.60       $1,032.5032   $1,032.51   $1,032.50   $1,032.50