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	$173.52	8.594%	$188.4323	$188.43	$188.45	$188.40
Purchase #2	$155.44	4.561%	$162.5296	$162.53	$162.55	$162.50
Purchase #3	$5.34	4.658%	$5.5887	$5.59	$5.60	$5.60
Purchase #4	$141.80	3.253%	$146.4128	$146.41	$146.40	$146.40
Purchase #5	$246.36	9.766%	$270.4195	$270.42	$270.40	$270.40
Purchase #6	$29.90	12.550%	$33.6525	$33.65	$33.65	$33.70
Purchase #7	$34.74	7.709%	$37.4181	$37.42	$37.40	$37.40
7 purchase totals =	$787.10		$844.4535	$844.45	$844.45	$844.40