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 $188.35   9.861%   $206.9232   $206.92   $206.90   $206.90  
  Purchase #2 $156.78   8.207%   $169.6469   $169.65   $169.65   $169.60  
  Purchase #3 $54.25   5.586%   $57.2804   $57.28   $57.30   $57.30  
  Purchase #4 $175.72   10.487%   $194.1478   $194.15   $194.15   $194.10  
  Purchase #5 $174.57   7.216%   $187.167   $187.17   $187.15   $187.20  
  Purchase #6 $119.70   12.661%   $134.8552   $134.86   $134.85   $134.90  
  Purchase #7 $225.53   13.368%   $255.6789   $255.68   $255.70   $255.70  
  7 purchase totals = $1,094.90       $1,205.6994   $1,205.71   $1,205.70   $1,205.70