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 $71.44   7.554%   $76.8366   $76.84   $76.85   $76.80  
  Purchase #2 $9.67   13.259%   $10.9521   $10.95   $10.95   $11.00  
  Purchase #3 $215.49   5.301%   $226.9131   $226.91   $226.90   $226.90  
  Purchase #4 $110.28   4.797%   $115.5701   $115.57   $115.55   $115.60  
  Purchase #5 $219.76   4.177%   $228.9394   $228.94   $228.95   $228.90  
  Purchase #6 $182.81   12.636%   $205.9099   $205.91   $205.90   $205.90  
  Purchase #7 $53.49   7.339%   $57.4156   $57.42   $57.40   $57.40  
  7 purchase totals = $862.94       $922.5368   $922.54   $922.50   $922.50