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	$76.38	9.335%	$83.5101	$83.51	$83.50	$83.50
Purchase #2	$226.52	3.363%	$234.1379	$234.14	$234.15	$234.10
Purchase #3	$157.31	6.820%	$168.0385	$168.04	$168.05	$168.00
Purchase #4	$66.89	9.427%	$73.1957	$73.20	$73.20	$73.20
Purchase #5	$65.72	8.336%	$71.1984	$71.20	$71.20	$71.20
Purchase #6	$129.65	7.306%	$139.1222	$139.12	$139.10	$139.10
Purchase #7	$97.80	8.208%	$105.8274	$105.83	$105.85	$105.80
7 purchase totals =	$820.27		$875.0302	$875.04	$875.05	$874.90