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	$47.76	10.756%	$52.8971	$52.90	$52.90	$52.90
Purchase #2	$142.72	3.851%	$148.2161	$148.22	$148.20	$148.20
Purchase #3	$233.58	13.375%	$264.8213	$264.82	$264.80	$264.80
Purchase #4	$29.72	13.805%	$33.8228	$33.82	$33.80	$33.80
Purchase #5	$120.85	11.294%	$134.4988	$134.50	$134.50	$134.50
Purchase #6	$146.34	8.138%	$158.2491	$158.25	$158.25	$158.20
Purchase #7	$64.41	7.849%	$69.4655	$69.47	$69.45	$69.50
7 purchase totals =	$785.38		$861.9707	$861.98	$861.90	$861.90