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	$47.92	6.593%	$51.0794	$51.08	$51.10	$51.10
Purchase #2	$155.46	10.488%	$171.7646	$171.76	$171.75	$171.80
Purchase #3	$85.71	4.634%	$89.6818	$89.68	$89.70	$89.70
Purchase #4	$194.45	7.803%	$209.6229	$209.62	$209.60	$209.60
Purchase #5	$209.88	12.840%	$236.8286	$236.83	$236.85	$236.80
Purchase #6	$93.70	6.212%	$99.5206	$99.52	$99.50	$99.50
Purchase #7	$44.33	3.229%	$45.7614	$45.76	$45.75	$45.80
7 purchase totals =	$831.45		$904.2593	$904.25	$904.25	$904.30