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	$35.33	6.518%	$37.6328	$37.63	$37.65	$37.60
Purchase #2	$81.63	8.795%	$88.8094	$88.81	$88.80	$88.80
Purchase #3	$58.99	11.170%	$65.5792	$65.58	$65.60	$65.60
Purchase #4	$18.61	13.345%	$21.0935	$21.09	$21.10	$21.10
Purchase #5	$152.62	12.855%	$172.2393	$172.24	$172.25	$172.20
Purchase #6	$131.89	11.778%	$147.424	$147.42	$147.40	$147.40
Purchase #7	$140.86	9.153%	$153.7529	$153.75	$153.75	$153.80
7 purchase totals =	$619.93		$686.5311	$686.52	$686.55	$686.50