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 $18.38   7.688%   $19.7931   $19.79   $19.80   $19.80  
  Purchase #2 $117.85   9.872%   $129.4842   $129.48   $129.50   $129.50  
  Purchase #3 $90.96   9.110%   $99.2465   $99.25   $99.25   $99.20  
  Purchase #4 $133.94   7.406%   $143.8596   $143.86   $143.85   $143.90  
  Purchase #5 $145.74   11.225%   $162.0993   $162.10   $162.10   $162.10  
  Purchase #6 $214.98   10.268%   $237.0541   $237.05   $237.05   $237.10  
  Purchase #7 $33.82   9.674%   $37.0917   $37.09   $37.10   $37.10  
  7 purchase totals = $755.67       $828.6285   $828.62   $828.65   $828.70