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	$226.50	8.188%	$245.0458	$245.05	$245.05	$245.00
Purchase #2	$89.89	5.491%	$94.8259	$94.83	$94.85	$94.80
Purchase #3	$42.92	13.374%	$48.6601	$48.66	$48.65	$48.70
Purchase #4	$137.28	11.765%	$153.431	$153.43	$153.45	$153.40
Purchase #5	$40.48	7.241%	$43.4112	$43.41	$43.40	$43.40
Purchase #6	$71.86	12.478%	$80.8267	$80.83	$80.85	$80.80
Purchase #7	$149.83	6.610%	$159.7338	$159.73	$159.75	$159.70
7 purchase totals =	$758.76		$825.9345	$825.94	$826.00	$825.80