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	$72.38	6.810%	$77.3091	$77.31	$77.30	$77.30
Purchase #2	$156.95	11.331%	$174.734	$174.73	$174.75	$174.70
Purchase #3	$67.78	4.380%	$70.7488	$70.75	$70.75	$70.70
Purchase #4	$151.45	13.169%	$171.3945	$171.39	$171.40	$171.40
Purchase #5	$107.99	6.308%	$114.802	$114.80	$114.80	$114.80
Purchase #6	$147.57	11.571%	$164.6453	$164.65	$164.65	$164.60
Purchase #7	$58.79	11.571%	$65.5926	$65.59	$65.60	$65.60
7 purchase totals =	$762.91		$839.2263	$839.22	$839.25	$839.10