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	$12.37	11.498%	$13.7923	$13.79	$13.80	$13.80
Purchase #2	$93.64	6.679%	$99.8942	$99.89	$99.90	$99.90
Purchase #3	$72.32	11.513%	$80.6462	$80.65	$80.65	$80.60
Purchase #4	$47.73	13.710%	$54.2738	$54.27	$54.25	$54.30
Purchase #5	$188.41	3.530%	$195.0609	$195.06	$195.05	$195.10
Purchase #6	$168.59	5.846%	$178.4458	$178.45	$178.45	$178.40
Purchase #7	$12.66	12.380%	$14.2273	$14.23	$14.25	$14.20
7 purchase totals =	$595.72		$636.3405	$636.34	$636.35	$636.30