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	$173.72	8.522%	$188.5244	$188.52	$188.50	$188.50
Purchase #2	$15.55	6.768%	$16.6024	$16.60	$16.60	$16.60
Purchase #3	$38.42	9.448%	$42.0499	$42.05	$42.05	$42.00
Purchase #4	$156.71	9.133%	$171.0223	$171.02	$171.00	$171.00
Purchase #5	$226.45	10.399%	$249.9985	$250.00	$250.00	$250.00
Purchase #6	$91.88	10.817%	$101.8187	$101.82	$101.80	$101.80
Purchase #7	$160.81	12.737%	$181.2924	$181.29	$181.30	$181.30
7 purchase totals =	$863.54		$951.3086	$951.30	$951.25	$951.20