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 $156.28   11.497%   $174.2475   $174.25   $174.25   $174.20  
  Purchase #2 $194.61   4.439%   $203.2487   $203.25   $203.25   $203.20  
  Purchase #3 $97.41   10.458%   $107.5971   $107.60   $107.60   $107.60  
  Purchase #4 $155.84   6.858%   $166.5275   $166.53   $166.55   $166.50  
  Purchase #5 $17.93   9.665%   $19.6629   $19.66   $19.65   $19.70  
  Purchase #6 $216.49   7.793%   $233.3611   $233.36   $233.35   $233.40  
  Purchase #7 $87.66   12.520%   $98.635   $98.64   $98.65   $98.60  
  7 purchase totals = $926.22       $1,003.2798   $1,003.29   $1,003.30   $1,003.20