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 $183.84   7.503%   $197.6335   $197.63   $197.65   $197.60  
  Purchase #2 $100.82   10.631%   $111.5382   $111.54   $111.55   $111.50  
  Purchase #3 $53.81   7.789%   $58.0013   $58.00   $58.00   $58.00  
  Purchase #4 $223.47   13.779%   $254.2619   $254.26   $254.25   $254.30  
  Purchase #5 $14.74   7.455%   $15.8389   $15.84   $15.85   $15.80  
  Purchase #6 $167.87   4.480%   $175.3906   $175.39   $175.40   $175.40  
  Purchase #7 $247.80   3.716%   $257.0082   $257.01   $257.00   $257.00  
  7 purchase totals = $992.35       $1,069.6726   $1,069.67   $1,069.70   $1,069.60