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 $193.25   6.559%   $205.9253   $205.93   $205.95   $205.90  
  Purchase #2 $77.83   12.474%   $87.5385   $87.54   $87.55   $87.50  
  Purchase #3 $53.73   4.143%   $55.956   $55.96   $55.95   $56.00  
  Purchase #4 $141.53   6.804%   $151.1597   $151.16   $151.15   $151.20  
  Purchase #5 $144.99   7.476%   $155.8295   $155.83   $155.85   $155.80  
  Purchase #6 $154.79   5.691%   $163.5991   $163.60   $163.60   $163.60  
  Purchase #7 $213.46   13.276%   $241.7989   $241.80   $241.80   $241.80  
  7 purchase totals = $979.58       $1,061.8070   $1,061.82   $1,061.85   $1,061.80