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 $193.73   10.287%   $213.659   $213.66   $213.65   $213.70  
  Purchase #2 $95.57   4.835%   $100.1908   $100.19   $100.20   $100.20  
  Purchase #3 $50.39   4.659%   $52.7377   $52.74   $52.75   $52.70  
  Purchase #4 $248.36   5.566%   $262.1837   $262.18   $262.20   $262.20  
  Purchase #5 $126.76   8.525%   $137.5663   $137.57   $137.55   $137.60  
  Purchase #6 $165.27   6.543%   $176.0836   $176.08   $176.10   $176.10  
  Purchase #7 $247.82   10.237%   $273.1893   $273.19   $273.20   $273.20  
  7 purchase totals = $1,127.90       $1,215.6104   $1,215.61   $1,215.65   $1,215.70