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 $203.46   8.427%   $220.6056   $220.61   $220.60   $220.60  
  Purchase #2 $95.34   3.634%   $98.8047   $98.80   $98.80   $98.80  
  Purchase #3 $153.43   3.745%   $159.176   $159.18   $159.20   $159.20  
  Purchase #4 $79.87   3.401%   $82.5864   $82.59   $82.60   $82.60  
  Purchase #5 $240.84   10.636%   $266.4557   $266.46   $266.45   $266.50  
  Purchase #6 $231.47   7.870%   $249.6867   $249.69   $249.70   $249.70  
  Purchase #7 $216.26   4.132%   $225.1959   $225.20   $225.20   $225.20  
  7 purchase totals = $1,220.67       $1,302.5110   $1,302.53   $1,302.55   $1,302.60