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	$136.55	3.689%	$141.5873	$141.59	$141.60	$141.60
Purchase #2	$37.98	9.592%	$41.623	$41.62	$41.60	$41.60
Purchase #3	$224.75	10.850%	$249.1354	$249.14	$249.15	$249.10
Purchase #4	$222.33	9.173%	$242.7243	$242.72	$242.70	$242.70
Purchase #5	$84.89	3.839%	$88.1489	$88.15	$88.15	$88.10
Purchase #6	$56.83	4.118%	$59.1703	$59.17	$59.15	$59.20
Purchase #7	$236.42	6.504%	$251.7968	$251.80	$251.80	$251.80
7 purchase totals =	$999.75		$1,074.1860	$1,074.19	$1,074.15	$1,074.10