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	$191.51	12.423%	$215.3013	$215.30	$215.30	$215.30
Purchase #2	$43.71	3.390%	$45.1918	$45.19	$45.20	$45.20
Purchase #3	$56.40	8.636%	$61.2707	$61.27	$61.25	$61.30
Purchase #4	$7.91	13.710%	$8.9945	$8.99	$9.00	$9.00
Purchase #5	$80.54	6.112%	$85.4626	$85.46	$85.45	$85.50
Purchase #6	$188.60	4.253%	$196.6212	$196.62	$196.60	$196.60
Purchase #7	$55.34	4.594%	$57.8823	$57.88	$57.90	$57.90
7 purchase totals =	$624.01		$670.7244	$670.71	$670.70	$670.80