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	$64.59	6.305%	$68.6624	$68.66	$68.65	$68.70
Purchase #2	$187.82	11.520%	$209.4569	$209.46	$209.45	$209.50
Purchase #3	$82.86	9.742%	$90.9322	$90.93	$90.95	$90.90
Purchase #4	$41.25	12.355%	$46.3464	$46.35	$46.35	$46.30
Purchase #5	$78.94	12.538%	$88.8375	$88.84	$88.85	$88.80
Purchase #6	$77.37	8.279%	$83.7755	$83.78	$83.80	$83.80
Purchase #7	$11.27	12.862%	$12.7195	$12.72	$12.70	$12.70
7 purchase totals =	$544.10		$600.7304	$600.74	$600.75	$600.70