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	$46.38	10.735%	$51.3589	$51.36	$51.35	$51.40
Purchase #2	$61.64	9.223%	$67.3251	$67.33	$67.35	$67.30
Purchase #3	$48.67	4.612%	$50.9147	$50.91	$50.90	$50.90
Purchase #4	$52.61	9.451%	$57.5822	$57.58	$57.60	$57.60
Purchase #5	$22.93	9.675%	$25.1485	$25.15	$25.15	$25.10
Purchase #6	$221.33	13.353%	$250.8842	$250.88	$250.90	$250.90
Purchase #7	$165.33	10.705%	$183.0286	$183.03	$183.05	$183.00
7 purchase totals =	$618.89		$686.2422	$686.24	$686.30	$686.20