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	$59.72	12.831%	$67.3827	$67.38	$67.40	$67.40
Purchase #2	$93.89	9.542%	$102.849	$102.85	$102.85	$102.80
Purchase #3	$76.83	11.227%	$85.4557	$85.46	$85.45	$85.50
Purchase #4	$24.45	6.395%	$26.0136	$26.01	$26.00	$26.00
Purchase #5	$28.75	10.212%	$31.686	$31.69	$31.70	$31.70
Purchase #6	$96.93	6.759%	$103.4815	$103.48	$103.50	$103.50
Purchase #7	$234.84	12.417%	$264.0001	$264.00	$264.00	$264.00
7 purchase totals =	$615.41		$680.8686	$680.87	$680.90	$680.90