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	$127.46	10.834%	$141.269	$141.27	$141.25	$141.30
Purchase #2	$169.34	13.515%	$192.2263	$192.23	$192.25	$192.20
Purchase #3	$89.93	9.424%	$98.405	$98.41	$98.40	$98.40
Purchase #4	$136.59	5.651%	$144.3087	$144.31	$144.30	$144.30
Purchase #5	$228.91	9.376%	$250.3726	$250.37	$250.35	$250.40
Purchase #6	$25.72	4.255%	$26.8144	$26.81	$26.80	$26.80
Purchase #7	$17.94	12.189%	$20.1267	$20.13	$20.15	$20.10
7 purchase totals =	$795.89		$873.5227	$873.53	$873.50	$873.50