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	$72.61	6.460%	$77.3006	$77.30	$77.30	$77.30
Purchase #2	$243.73	12.693%	$274.6666	$274.67	$274.65	$274.70
Purchase #3	$135.85	6.160%	$144.2184	$144.22	$144.20	$144.20
Purchase #4	$209.39	5.188%	$220.2532	$220.25	$220.25	$220.30
Purchase #5	$139.44	13.736%	$158.5935	$158.59	$158.60	$158.60
Purchase #6	$237.57	7.543%	$255.4899	$255.49	$255.50	$255.50
Purchase #7	$22.62	11.788%	$25.2864	$25.29	$25.30	$25.30
7 purchase totals =	$1,061.21		$1,155.8086	$1,155.81	$1,155.80	$1,155.90