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	$166.52	11.470%	$185.6198	$185.62	$185.60	$185.60
Purchase #2	$159.42	13.328%	$180.6675	$180.67	$180.65	$180.70
Purchase #3	$64.84	11.275%	$72.1507	$72.15	$72.15	$72.20
Purchase #4	$221.30	3.474%	$228.988	$228.99	$229.00	$229.00
Purchase #5	$52.27	4.404%	$54.572	$54.57	$54.55	$54.60
Purchase #6	$88.36	11.804%	$98.79	$98.79	$98.80	$98.80
Purchase #7	$242.74	6.664%	$258.9162	$258.92	$258.90	$258.90
7 purchase totals =	$995.45		$1,079.7042	$1,079.71	$1,079.65	$1,079.80