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	$95.58	4.453%	$99.8362	$99.84	$99.85	$99.80
Purchase #2	$42.90	10.617%	$47.4547	$47.45	$47.45	$47.50
Purchase #3	$64.39	9.227%	$70.3313	$70.33	$70.35	$70.30
Purchase #4	$176.50	6.221%	$187.4801	$187.48	$187.50	$187.50
Purchase #5	$105.82	4.856%	$110.9586	$110.96	$110.95	$111.00
Purchase #6	$53.87	10.864%	$59.7224	$59.72	$59.70	$59.70
Purchase #7	$122.69	10.456%	$135.5185	$135.52	$135.50	$135.50
7 purchase totals =	$661.75		$711.3018	$711.30	$711.30	$711.30