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	$246.25	12.580%	$277.2283	$277.23	$277.25	$277.20
Purchase #2	$59.52	8.670%	$64.6804	$64.68	$64.70	$64.70
Purchase #3	$170.61	6.264%	$181.297	$181.30	$181.30	$181.30
Purchase #4	$18.80	7.222%	$20.1577	$20.16	$20.15	$20.20
Purchase #5	$166.84	7.421%	$179.2212	$179.22	$179.20	$179.20
Purchase #6	$48.84	8.138%	$52.8146	$52.81	$52.80	$52.80
Purchase #7	$56.90	5.289%	$59.9094	$59.91	$59.90	$59.90
7 purchase totals =	$767.76		$835.3086	$835.31	$835.30	$835.30