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 $201.82   3.357%   $208.5951   $208.60   $208.60   $208.60  
  Purchase #2 $61.74   7.124%   $66.1384   $66.14   $66.15   $66.10  
  Purchase #3 $111.48   4.556%   $116.559   $116.56   $116.55   $116.60  
  Purchase #4 $124.69   13.578%   $141.6204   $141.62   $141.60   $141.60  
  Purchase #5 $133.51   13.275%   $151.2335   $151.23   $151.25   $151.20  
  Purchase #6 $220.67   11.193%   $245.3696   $245.37   $245.35   $245.40  
  Purchase #7 $196.87   4.801%   $206.3217   $206.32   $206.30   $206.30  
  7 purchase totals = $1,050.78       $1,135.8377   $1,135.84   $1,135.80   $1,135.80