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	$113.80	12.654%	$128.2003	$128.20	$128.20	$128.20
Purchase #2	$30.91	5.131%	$32.496	$32.50	$32.50	$32.50
Purchase #3	$67.73	6.523%	$72.148	$72.15	$72.15	$72.10
Purchase #4	$84.50	4.220%	$88.0659	$88.07	$88.05	$88.10
Purchase #5	$127.72	3.637%	$132.3652	$132.37	$132.35	$132.40
Purchase #6	$104.95	6.489%	$111.7602	$111.76	$111.75	$111.80
Purchase #7	$250.27	11.371%	$278.7282	$278.73	$278.75	$278.70
7 purchase totals =	$779.88		$843.7638	$843.78	$843.75	$843.80