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 $201.77   8.145%   $218.2042   $218.20   $218.20   $218.20  
  Purchase #2 $223.74   12.153%   $250.9311   $250.93   $250.95   $250.90  
  Purchase #3 $67.27   13.323%   $76.2324   $76.23   $76.25   $76.20  
  Purchase #4 $40.70   7.341%   $43.6878   $43.69   $43.70   $43.70  
  Purchase #5 $183.63   12.540%   $206.6572   $206.66   $206.65   $206.70  
  Purchase #6 $221.57   6.563%   $236.1116   $236.11   $236.10   $236.10  
  Purchase #7 $118.88   5.329%   $125.2151   $125.22   $125.20   $125.20  
  7 purchase totals = $1,057.56       $1,157.0394   $1,157.04   $1,157.05   $1,157.00