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 $207.78   12.528%   $233.8107   $233.81   $233.80   $233.80  
  Purchase #2 $59.51   10.217%   $65.5901   $65.59   $65.60   $65.60  
  Purchase #3 $16.51   6.840%   $17.6393   $17.64   $17.65   $17.60  
  Purchase #4 $108.51   13.277%   $122.9169   $122.92   $122.90   $122.90  
  Purchase #5 $153.49   11.475%   $171.103   $171.10   $171.10   $171.10  
  Purchase #6 $193.30   4.306%   $201.6235   $201.62   $201.60   $201.60  
  Purchase #7 $17.25   13.514%   $19.5812   $19.58   $19.60   $19.60  
  7 purchase totals = $756.35       $832.2647   $832.26   $832.25   $832.20