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	$169.88	5.450%	$179.1385	$179.14	$179.15	$179.10
Purchase #2	$117.69	9.223%	$128.5445	$128.54	$128.55	$128.50
Purchase #3	$213.81	9.532%	$234.1904	$234.19	$234.20	$234.20
Purchase #4	$183.62	4.277%	$191.4734	$191.47	$191.45	$191.50
Purchase #5	$96.44	12.459%	$108.4555	$108.46	$108.45	$108.50
Purchase #6	$38.93	8.553%	$42.2597	$42.26	$42.25	$42.30
Purchase #7	$50.57	13.579%	$57.4369	$57.44	$57.45	$57.40
7 purchase totals =	$870.94		$941.4989	$941.50	$941.50	$941.50