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 $155.42   5.691%   $164.265   $164.27   $164.25   $164.30  
  Purchase #2 $186.52   4.767%   $195.4114   $195.41   $195.40   $195.40  
  Purchase #3 $19.97   13.392%   $22.6444   $22.64   $22.65   $22.60  
  Purchase #4 $149.74   6.247%   $159.0943   $159.09   $159.10   $159.10  
  Purchase #5 $186.72   3.437%   $193.1376   $193.14   $193.15   $193.10  
  Purchase #6 $241.27   3.384%   $249.4346   $249.43   $249.45   $249.40  
  Purchase #7 $11.84   12.647%   $13.3374   $13.34   $13.35   $13.30  
  7 purchase totals = $951.48       $997.3247   $997.32   $997.35   $997.20