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 $66.90   13.480%   $75.9181   $75.92   $75.90   $75.90  
  Purchase #2 $56.57   9.247%   $61.801   $61.80   $61.80   $61.80  
  Purchase #3 $52.90   8.767%   $57.5377   $57.54   $57.55   $57.50  
  Purchase #4 $27.97   6.194%   $29.7025   $29.70   $29.70   $29.70  
  Purchase #5 $115.85   13.189%   $131.1295   $131.13   $131.15   $131.10  
  Purchase #6 $169.80   8.767%   $184.6864   $184.69   $184.70   $184.70  
  Purchase #7 $16.33   10.421%   $18.0317   $18.03   $18.05   $18.00  
  7 purchase totals = $506.32       $558.8069   $558.81   $558.85   $558.70