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	$198.92	11.764%	$222.3209	$222.32	$222.30	$222.30
Purchase #2	$249.65	3.203%	$257.6463	$257.65	$257.65	$257.60
Purchase #3	$7.83	8.381%	$8.4862	$8.49	$8.50	$8.50
Purchase #4	$48.72	4.305%	$50.8174	$50.82	$50.80	$50.80
Purchase #5	$50.93	4.474%	$53.2086	$53.21	$53.20	$53.20
Purchase #6	$30.41	6.281%	$32.3201	$32.32	$32.30	$32.30
Purchase #7	$178.84	3.729%	$185.5089	$185.51	$185.50	$185.50
7 purchase totals =	$765.30		$810.3084	$810.32	$810.25	$810.20