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	$40.49	4.543%	$42.3295	$42.33	$42.35	$42.30
Purchase #2	$197.65	13.580%	$224.4909	$224.49	$224.50	$224.50
Purchase #3	$30.41	8.486%	$32.9906	$32.99	$33.00	$33.00
Purchase #4	$69.76	3.713%	$72.3502	$72.35	$72.35	$72.40
Purchase #5	$48.89	4.788%	$51.2309	$51.23	$51.25	$51.20
Purchase #6	$109.82	6.730%	$117.2109	$117.21	$117.20	$117.20
Purchase #7	$35.78	13.622%	$40.654	$40.65	$40.65	$40.70
7 purchase totals =	$532.80		$581.2570	$581.25	$581.30	$581.30