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	$42.57	13.461%	$48.3003	$48.30	$48.30	$48.30
Purchase #2	$58.31	13.715%	$66.3072	$66.31	$66.30	$66.30
Purchase #3	$179.42	10.596%	$198.4313	$198.43	$198.45	$198.40
Purchase #4	$21.38	3.464%	$22.1206	$22.12	$22.10	$22.10
Purchase #5	$178.54	3.488%	$184.7675	$184.77	$184.75	$184.80
Purchase #6	$61.43	9.166%	$67.0607	$67.06	$67.05	$67.10
Purchase #7	$91.70	8.572%	$99.5605	$99.56	$99.55	$99.60
7 purchase totals =	$633.35		$686.5481	$686.55	$686.50	$686.60