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 $226.81   6.508%   $241.5708   $241.57   $241.55   $241.60  
  Purchase #2 $115.31   6.333%   $122.6126   $122.61   $122.60   $122.60  
  Purchase #3 $16.57   12.818%   $18.6939   $18.69   $18.70   $18.70  
  Purchase #4 $87.99   13.286%   $99.6804   $99.68   $99.70   $99.70  
  Purchase #5 $201.80   6.325%   $214.5639   $214.56   $214.55   $214.60  
  Purchase #6 $65.51   8.549%   $71.1104   $71.11   $71.10   $71.10  
  Purchase #7 $31.25   6.494%   $33.2794   $33.28   $33.30   $33.30  
  7 purchase totals = $745.24       $801.5114   $801.50   $801.50   $801.60