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 $56.29   4.748%   $58.9626   $58.96   $58.95   $59.00  
  Purchase #2 $140.69   10.311%   $155.1965   $155.20   $155.20   $155.20  
  Purchase #3 $35.80   8.236%   $38.7485   $38.75   $38.75   $38.70  
  Purchase #4 $52.61   7.104%   $56.3474   $56.35   $56.35   $56.30  
  Purchase #5 $223.32   12.467%   $251.1613   $251.16   $251.15   $251.20  
  Purchase #6 $203.59   5.365%   $214.5126   $214.51   $214.50   $214.50  
  Purchase #7 $90.67   5.152%   $95.3413   $95.34   $95.35   $95.30  
  7 purchase totals = $802.97       $870.2702   $870.27   $870.25   $870.20