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 $49.92   12.252%   $56.0362   $56.04   $56.05   $56.00  
  Purchase #2 $103.44   3.305%   $106.8587   $106.86   $106.85   $106.90  
  Purchase #3 $156.39   5.668%   $165.2542   $165.25   $165.25   $165.30  
  Purchase #4 $200.48   9.105%   $218.7337   $218.73   $218.75   $218.70  
  Purchase #5 $166.81   11.351%   $185.7446   $185.74   $185.75   $185.70  
  Purchase #6 $196.75   13.755%   $223.813   $223.81   $223.80   $223.80  
  Purchase #7 $86.95   9.562%   $95.2642   $95.26   $95.25   $95.30  
  7 purchase totals = $960.74       $1,051.7046   $1,051.69   $1,051.70   $1,051.70