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	$70.51	12.517%	$79.3357	$79.34	$79.35	$79.30
Purchase #2	$50.62	7.694%	$54.5147	$54.51	$54.50	$54.50
Purchase #3	$158.56	4.503%	$165.7	$165.70	$165.70	$165.70
Purchase #4	$154.64	11.632%	$172.6277	$172.63	$172.65	$172.60
Purchase #5	$187.64	11.810%	$209.8003	$209.80	$209.80	$209.80
Purchase #6	$218.32	13.600%	$248.0115	$248.01	$248.00	$248.00
Purchase #7	$222.34	6.800%	$237.4591	$237.46	$237.45	$237.50
7 purchase totals =	$1,062.63		$1,167.4490	$1,167.45	$1,167.45	$1,167.40