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	$7.81	5.356%	$8.2283	$8.23	$8.25	$8.20
Purchase #2	$99.42	12.503%	$111.8505	$111.85	$111.85	$111.90
Purchase #3	$13.43	10.871%	$14.89	$14.89	$14.90	$14.90
Purchase #4	$54.29	11.341%	$60.447	$60.45	$60.45	$60.40
Purchase #5	$233.35	7.328%	$250.4499	$250.45	$250.45	$250.40
Purchase #6	$126.51	10.447%	$139.7265	$139.73	$139.75	$139.70
Purchase #7	$250.73	8.350%	$271.666	$271.67	$271.65	$271.70
7 purchase totals =	$785.54		$857.2582	$857.27	$857.30	$857.20