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 $226.87   11.160%   $252.1887   $252.19   $252.20   $252.20  
  Purchase #2 $242.85   10.559%   $268.4925   $268.49   $268.50   $268.50  
  Purchase #3 $154.76   12.702%   $174.4176   $174.42   $174.40   $174.40  
  Purchase #4 $242.42   5.794%   $256.4658   $256.47   $256.45   $256.50  
  Purchase #5 $162.73   13.792%   $185.1737   $185.17   $185.15   $185.20  
  Purchase #6 $9.33   5.444%   $9.8379   $9.84   $9.85   $9.80  
  Purchase #7 $218.35   13.424%   $247.6613   $247.66   $247.65   $247.70  
  7 purchase totals = $1,257.31       $1,394.2375   $1,394.24   $1,394.20   $1,394.30