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 $51.49   5.362%   $54.2509   $54.25   $54.25   $54.30  
  Purchase #2 $113.57   11.723%   $126.8838   $126.88   $126.90   $126.90  
  Purchase #3 $199.49   3.530%   $206.532   $206.53   $206.55   $206.50  
  Purchase #4 $183.67   6.753%   $196.0732   $196.07   $196.05   $196.10  
  Purchase #5 $47.43   3.812%   $49.238   $49.24   $49.25   $49.20  
  Purchase #6 $131.71   6.670%   $140.4951   $140.50   $140.50   $140.50  
  Purchase #7 $204.59   3.470%   $211.6893   $211.69   $211.70   $211.70  
  7 purchase totals = $931.95       $985.1623   $985.16   $985.20   $985.20