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 $157.50   11.632%   $175.8204   $175.82   $175.80   $175.80  
  Purchase #2 $208.37   6.785%   $222.5079   $222.51   $222.50   $222.50  
  Purchase #3 $98.26   6.766%   $104.9083   $104.91   $104.90   $104.90  
  Purchase #4 $117.69   4.288%   $122.7365   $122.74   $122.75   $122.70  
  Purchase #5 $9.95   3.797%   $10.3278   $10.33   $10.35   $10.30  
  Purchase #6 $245.30   10.407%   $270.8284   $270.83   $270.85   $270.80  
  Purchase #7 $103.59   13.440%   $117.5125   $117.51   $117.50   $117.50  
  7 purchase totals = $940.66       $1,024.6418   $1,024.65   $1,024.65   $1,024.50