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	$47.80	13.285%	$54.1502	$54.15	$54.15	$54.20
Purchase #2	$237.74	7.580%	$255.7607	$255.76	$255.75	$255.80
Purchase #3	$59.43	3.872%	$61.7311	$61.73	$61.75	$61.70
Purchase #4	$139.52	11.838%	$156.0364	$156.04	$156.05	$156.00
Purchase #5	$66.86	5.409%	$70.4765	$70.48	$70.50	$70.50
Purchase #6	$93.64	11.552%	$104.4573	$104.46	$104.45	$104.50
Purchase #7	$167.87	7.103%	$179.7938	$179.79	$179.80	$179.80
7 purchase totals =	$812.86		$882.4060	$882.41	$882.45	$882.50