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 $68.91   5.627%   $72.7876   $72.79   $72.80   $72.80  
  Purchase #2 $244.34   9.279%   $267.0123   $267.01   $267.00   $267.00  
  Purchase #3 $218.87   5.425%   $230.7437   $230.74   $230.75   $230.70  
  Purchase #4 $121.61   3.292%   $125.6134   $125.61   $125.60   $125.60  
  Purchase #5 $90.28   9.411%   $98.7763   $98.78   $98.80   $98.80  
  Purchase #6 $185.97   11.205%   $206.8079   $206.81   $206.80   $206.80  
  Purchase #7 $127.44   4.388%   $133.0321   $133.03   $133.05   $133.00  
  7 purchase totals = $1,057.42       $1,134.7733   $1,134.77   $1,134.80   $1,134.70