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	$116.40	6.592%	$124.0731	$124.07	$124.05	$124.10
Purchase #2	$114.91	4.825%	$120.4544	$120.45	$120.45	$120.50
Purchase #3	$250.31	10.866%	$277.5087	$277.51	$277.50	$277.50
Purchase #4	$52.78	13.318%	$59.8092	$59.81	$59.80	$59.80
Purchase #5	$209.96	6.259%	$223.1014	$223.10	$223.10	$223.10
Purchase #6	$50.68	9.657%	$55.5742	$55.57	$55.55	$55.60
Purchase #7	$154.38	3.294%	$159.4653	$159.47	$159.45	$159.50
7 purchase totals =	$949.42		$1,019.9863	$1,019.98	$1,019.90	$1,020.10