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 $109.51   11.582%   $122.1934   $122.19   $122.20   $122.20  
  Purchase #2 $168.88   5.703%   $178.5112   $178.51   $178.50   $178.50  
  Purchase #3 $210.95   3.196%   $217.692   $217.69   $217.70   $217.70  
  Purchase #4 $85.56   12.425%   $96.1908   $96.19   $96.20   $96.20  
  Purchase #5 $60.53   8.476%   $65.6605   $65.66   $65.65   $65.70  
  Purchase #6 $241.51   3.471%   $249.8928   $249.89   $249.90   $249.90  
  Purchase #7 $199.48   12.571%   $224.5566   $224.56   $224.55   $224.60  
  7 purchase totals = $1,076.42       $1,154.6973   $1,154.69   $1,154.70   $1,154.80