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	$239.68	6.300%	$254.7798	$254.78	$254.80	$254.80
Purchase #2	$79.61	12.368%	$89.4562	$89.46	$89.45	$89.50
Purchase #3	$210.51	11.827%	$235.407	$235.41	$235.40	$235.40
Purchase #4	$84.39	10.743%	$93.456	$93.46	$93.45	$93.50
Purchase #5	$177.83	5.869%	$188.2668	$188.27	$188.25	$188.30
Purchase #6	$192.96	8.827%	$209.9926	$209.99	$210.00	$210.00
Purchase #7	$8.91	13.813%	$10.1407	$10.14	$10.15	$10.10
7 purchase totals =	$993.89		$1,081.4991	$1,081.51	$1,081.50	$1,081.60