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 $183.57   5.635%   $193.9142   $193.91   $193.90   $193.90  
  Purchase #2 $74.61   7.135%   $79.9334   $79.93   $79.95   $79.90  
  Purchase #3 $161.54   5.714%   $170.7704   $170.77   $170.75   $170.80  
  Purchase #4 $32.38   10.700%   $35.8447   $35.84   $35.85   $35.80  
  Purchase #5 $187.96   6.109%   $199.4425   $199.44   $199.45   $199.40  
  Purchase #6 $234.95   4.186%   $244.785   $244.79   $244.80   $244.80  
  Purchase #7 $98.76   3.464%   $102.181   $102.18   $102.20   $102.20  
  7 purchase totals = $973.77       $1,026.8712   $1,026.86   $1,026.90   $1,026.80