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	$171.92	8.212%	$186.0381	$186.04	$186.05	$186.00
Purchase #2	$33.45	11.296%	$37.2285	$37.23	$37.25	$37.20
Purchase #3	$37.52	12.585%	$42.2419	$42.24	$42.25	$42.20
Purchase #4	$18.59	8.519%	$20.1737	$20.17	$20.15	$20.20
Purchase #5	$247.76	13.363%	$280.8682	$280.87	$280.85	$280.90
Purchase #6	$21.85	4.229%	$22.774	$22.77	$22.75	$22.80
Purchase #7	$33.59	11.438%	$37.432	$37.43	$37.45	$37.40
7 purchase totals =	$564.68		$626.7564	$626.75	$626.75	$626.70