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	$111.70	12.366%	$125.5128	$125.51	$125.50	$125.50
Purchase #2	$231.45	11.232%	$257.4465	$257.45	$257.45	$257.40
Purchase #3	$70.69	7.555%	$76.0306	$76.03	$76.05	$76.00
Purchase #4	$123.28	6.854%	$131.7296	$131.73	$131.75	$131.70
Purchase #5	$191.74	9.487%	$209.9304	$209.93	$209.95	$209.90
Purchase #6	$52.91	12.494%	$59.5206	$59.52	$59.50	$59.50
Purchase #7	$47.46	12.853%	$53.56	$53.56	$53.55	$53.60
7 purchase totals =	$829.23		$913.7305	$913.73	$913.75	$913.60