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	$157.36	13.217%	$178.1583	$178.16	$178.15	$178.20
Purchase #2	$53.70	6.220%	$57.0401	$57.04	$57.05	$57.00
Purchase #3	$30.48	13.138%	$34.4845	$34.48	$34.50	$34.50
Purchase #4	$191.33	4.182%	$199.3314	$199.33	$199.35	$199.30
Purchase #5	$99.25	13.748%	$112.8949	$112.89	$112.90	$112.90
Purchase #6	$247.39	11.332%	$275.4242	$275.42	$275.40	$275.40
Purchase #7	$55.48	7.751%	$59.7803	$59.78	$59.80	$59.80
7 purchase totals =	$834.99		$917.1137	$917.10	$917.15	$917.10