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 $93.71   4.611%   $98.031   $98.03   $98.05   $98.00  
  Purchase #2 $41.48   13.506%   $47.0823   $47.08   $47.10   $47.10  
  Purchase #3 $146.29   7.847%   $157.7694   $157.77   $157.75   $157.80  
  Purchase #4 $229.75   6.553%   $244.8055   $244.81   $244.80   $244.80  
  Purchase #5 $229.74   9.575%   $251.7376   $251.74   $251.75   $251.70  
  Purchase #6 $29.84   5.686%   $31.5367   $31.54   $31.55   $31.50  
  Purchase #7 $14.82   3.158%   $15.288   $15.29   $15.30   $15.30  
  7 purchase totals = $785.63       $846.2505   $846.26   $846.30   $846.20