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	$74.77	6.680%	$79.7646	$79.76	$79.75	$79.80
Purchase #2	$141.72	7.127%	$151.8204	$151.82	$151.80	$151.80
Purchase #3	$223.49	13.411%	$253.4622	$253.46	$253.45	$253.50
Purchase #4	$131.90	12.341%	$148.1778	$148.18	$148.20	$148.20
Purchase #5	$220.73	12.681%	$248.7208	$248.72	$248.70	$248.70
Purchase #6	$100.69	8.617%	$109.3665	$109.37	$109.35	$109.40
Purchase #7	$240.95	13.826%	$274.2637	$274.26	$274.25	$274.30
7 purchase totals =	$1,134.25		$1,265.5760	$1,265.57	$1,265.50	$1,265.70