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 $84.57   13.836%   $96.2711   $96.27   $96.25   $96.30  
  Purchase #2 $241.31   3.525%   $249.8162   $249.82   $249.80   $249.80  
  Purchase #3 $233.92   4.806%   $245.1622   $245.16   $245.15   $245.20  
  Purchase #4 $105.64   4.611%   $110.5111   $110.51   $110.50   $110.50  
  Purchase #5 $153.86   7.864%   $165.9596   $165.96   $165.95   $166.00  
  Purchase #6 $181.97   3.772%   $188.8339   $188.83   $188.85   $188.80  
  Purchase #7 $60.36   4.712%   $63.2042   $63.20   $63.20   $63.20  
  7 purchase totals = $1,061.63       $1,119.7583   $1,119.75   $1,119.70   $1,119.80