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	$229.38	8.741%	$249.4301	$249.43	$249.45	$249.40
Purchase #2	$19.70	3.745%	$20.4378	$20.44	$20.45	$20.40
Purchase #3	$105.39	10.108%	$116.0428	$116.04	$116.05	$116.00
Purchase #4	$85.45	12.729%	$96.3269	$96.33	$96.35	$96.30
Purchase #5	$83.37	13.251%	$94.4174	$94.42	$94.40	$94.40
Purchase #6	$97.31	3.250%	$100.4726	$100.47	$100.45	$100.50
Purchase #7	$180.37	12.857%	$203.5602	$203.56	$203.55	$203.60
7 purchase totals =	$800.97		$880.6878	$880.69	$880.70	$880.60