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	$93.46	6.813%	$99.8274	$99.83	$99.85	$99.80
Purchase #2	$45.90	9.305%	$50.171	$50.17	$50.15	$50.20
Purchase #3	$99.39	6.372%	$105.7231	$105.72	$105.70	$105.70
Purchase #4	$195.72	13.637%	$222.4103	$222.41	$222.40	$222.40
Purchase #5	$23.27	10.173%	$25.6373	$25.64	$25.65	$25.60
Purchase #6	$62.43	12.411%	$70.1782	$70.18	$70.20	$70.20
Purchase #7	$149.80	5.415%	$157.9117	$157.91	$157.90	$157.90
7 purchase totals =	$669.97		$731.8590	$731.86	$731.85	$731.80