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	$87.35	13.669%	$99.2899	$99.29	$99.30	$99.30
Purchase #2	$9.70	3.566%	$10.0459	$10.05	$10.05	$10.00
Purchase #3	$67.76	4.455%	$70.7787	$70.78	$70.80	$70.80
Purchase #4	$77.38	8.272%	$83.7809	$83.78	$83.80	$83.80
Purchase #5	$57.46	6.755%	$61.3414	$61.34	$61.35	$61.30
Purchase #6	$239.66	6.289%	$254.7322	$254.73	$254.75	$254.70
Purchase #7	$234.57	13.233%	$265.6106	$265.61	$265.60	$265.60
7 purchase totals =	$773.88		$845.5796	$845.58	$845.65	$845.50