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	$121.50	12.853%	$137.1164	$137.12	$137.10	$137.10
Purchase #2	$32.63	9.190%	$35.6287	$35.63	$35.65	$35.60
Purchase #3	$146.75	13.166%	$166.0711	$166.07	$166.05	$166.10
Purchase #4	$239.58	10.375%	$264.4364	$264.44	$264.45	$264.40
Purchase #5	$149.90	8.229%	$162.2353	$162.24	$162.25	$162.20
Purchase #6	$101.46	7.576%	$109.1466	$109.15	$109.15	$109.10
Purchase #7	$233.32	13.487%	$264.7879	$264.79	$264.80	$264.80
7 purchase totals =	$1,025.14		$1,139.4224	$1,139.44	$1,139.45	$1,139.30