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	$154.49	9.338%	$168.9163	$168.92	$168.90	$168.90
Purchase #2	$109.93	12.762%	$123.9593	$123.96	$123.95	$124.00
Purchase #3	$141.80	11.596%	$158.2431	$158.24	$158.25	$158.20
Purchase #4	$119.66	6.534%	$127.4786	$127.48	$127.50	$127.50
Purchase #5	$208.91	3.757%	$216.7587	$216.76	$216.75	$216.80
Purchase #6	$20.46	3.337%	$21.1428	$21.14	$21.15	$21.10
Purchase #7	$12.70	4.165%	$13.229	$13.23	$13.25	$13.20
7 purchase totals =	$767.95		$829.7278	$829.73	$829.75	$829.70