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 $195.49   3.670%   $202.6645   $202.66   $202.65   $202.70  
  Purchase #2 $16.95   9.621%   $18.5808   $18.58   $18.60   $18.60  
  Purchase #3 $177.27   8.396%   $192.1536   $192.15   $192.15   $192.20  
  Purchase #4 $69.32   9.398%   $75.8347   $75.83   $75.85   $75.80  
  Purchase #5 $237.55   5.161%   $249.81   $249.81   $249.80   $249.80  
  Purchase #6 $71.29   12.750%   $80.3795   $80.38   $80.40   $80.40  
  Purchase #7 $131.35   7.192%   $140.7967   $140.80   $140.80   $140.80  
  7 purchase totals = $899.22       $960.2198   $960.21   $960.25   $960.30