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	$196.43	6.497%	$209.1921	$209.19	$209.20	$209.20
Purchase #2	$169.72	6.240%	$180.3105	$180.31	$180.30	$180.30
Purchase #3	$57.51	4.192%	$59.9208	$59.92	$59.90	$59.90
Purchase #4	$92.62	3.243%	$95.6237	$95.62	$95.60	$95.60
Purchase #5	$70.25	8.244%	$76.0414	$76.04	$76.05	$76.00
Purchase #6	$192.80	11.577%	$215.1205	$215.12	$215.10	$215.10
Purchase #7	$20.89	7.367%	$22.429	$22.43	$22.45	$22.40
7 purchase totals =	$800.22		$858.6380	$858.63	$858.60	$858.50