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	$124.73	11.667%	$139.2822	$139.28	$139.30	$139.30
Purchase #2	$83.57	12.361%	$93.9001	$93.90	$93.90	$93.90
Purchase #3	$12.82	5.751%	$13.5573	$13.56	$13.55	$13.60
Purchase #4	$151.72	4.220%	$158.1226	$158.12	$158.10	$158.10
Purchase #5	$128.41	12.492%	$144.451	$144.45	$144.45	$144.50
Purchase #6	$187.53	6.405%	$199.5413	$199.54	$199.55	$199.50
Purchase #7	$249.35	9.757%	$273.6791	$273.68	$273.70	$273.70
7 purchase totals =	$938.13		$1,022.5336	$1,022.53	$1,022.55	$1,022.60