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	$159.69	11.820%	$178.5654	$178.57	$178.55	$178.60
Purchase #2	$234.64	6.669%	$250.2881	$250.29	$250.30	$250.30
Purchase #3	$236.95	4.455%	$247.5061	$247.51	$247.50	$247.50
Purchase #4	$150.31	13.437%	$170.5072	$170.51	$170.50	$170.50
Purchase #5	$148.56	13.243%	$168.2338	$168.23	$168.25	$168.20
Purchase #6	$29.79	8.468%	$32.3126	$32.31	$32.30	$32.30
Purchase #7	$42.88	12.499%	$48.2396	$48.24	$48.25	$48.20
7 purchase totals =	$1,002.82		$1,095.6528	$1,095.66	$1,095.65	$1,095.60