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	$42.55	6.243%	$45.2064	$45.21	$45.20	$45.20
Purchase #2	$160.34	5.354%	$168.9246	$168.92	$168.90	$168.90
Purchase #3	$121.74	11.837%	$136.1504	$136.15	$136.15	$136.20
Purchase #4	$40.69	6.228%	$43.2242	$43.22	$43.20	$43.20
Purchase #5	$166.85	4.698%	$174.6886	$174.69	$174.70	$174.70
Purchase #6	$123.82	5.142%	$130.1868	$130.19	$130.20	$130.20
Purchase #7	$76.55	6.431%	$81.4729	$81.47	$81.45	$81.50
7 purchase totals =	$732.54		$779.8539	$779.85	$779.80	$779.90