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 $160.66   12.533%   $180.7955   $180.80   $180.80   $180.80  
  Purchase #2 $21.28   3.515%   $22.028   $22.03   $22.05   $22.00  
  Purchase #3 $123.50   10.615%   $136.6095   $136.61   $136.60   $136.60  
  Purchase #4 $198.71   7.873%   $214.3544   $214.35   $214.35   $214.40  
  Purchase #5 $14.38   7.489%   $15.4569   $15.46   $15.45   $15.50  
  Purchase #6 $148.66   10.155%   $163.7564   $163.76   $163.75   $163.80  
  Purchase #7 $139.63   7.687%   $150.3634   $150.36   $150.35   $150.40  
  7 purchase totals = $806.82       $883.3641   $883.37   $883.35   $883.50