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 $239.92   12.241%   $269.2886   $269.29   $269.30   $269.30  
  Purchase #2 $162.76   8.336%   $176.3277   $176.33   $176.35   $176.30  
  Purchase #3 $186.33   6.214%   $197.9085   $197.91   $197.90   $197.90  
  Purchase #4 $20.74   12.420%   $23.3159   $23.32   $23.30   $23.30  
  Purchase #5 $145.86   12.636%   $164.2909   $164.29   $164.30   $164.30  
  Purchase #6 $181.31   9.129%   $197.8618   $197.86   $197.85   $197.90  
  Purchase #7 $61.88   7.450%   $66.4901   $66.49   $66.50   $66.50  
  7 purchase totals = $998.80       $1,095.4835   $1,095.49   $1,095.50   $1,095.50