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	$38.35	4.623%	$40.1229	$40.12	$40.10	$40.10
Purchase #2	$58.49	13.710%	$66.509	$66.51	$66.50	$66.50
Purchase #3	$13.56	11.737%	$15.1515	$15.15	$15.15	$15.20
Purchase #4	$120.81	6.845%	$129.0794	$129.08	$129.10	$129.10
Purchase #5	$189.82	5.773%	$200.7783	$200.78	$200.80	$200.80
Purchase #6	$67.30	7.604%	$72.4175	$72.42	$72.40	$72.40
Purchase #7	$202.78	12.502%	$228.1316	$228.13	$228.15	$228.10
7 purchase totals =	$691.11		$752.1902	$752.19	$752.20	$752.20