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	$99.54	13.256%	$112.735	$112.74	$112.75	$112.70
Purchase #2	$81.40	10.260%	$89.7516	$89.75	$89.75	$89.80
Purchase #3	$90.72	5.250%	$95.4828	$95.48	$95.50	$95.50
Purchase #4	$136.30	10.397%	$150.4711	$150.47	$150.45	$150.50
Purchase #5	$178.75	4.267%	$186.3773	$186.38	$186.40	$186.40
Purchase #6	$222.47	9.192%	$242.9194	$242.92	$242.90	$242.90
Purchase #7	$13.95	8.218%	$15.0964	$15.10	$15.10	$15.10
7 purchase totals =	$823.13		$892.8336	$892.84	$892.85	$892.90