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	$54.75	4.234%	$57.0681	$57.07	$57.05	$57.10
Purchase #2	$91.83	3.584%	$95.1212	$95.12	$95.10	$95.10
Purchase #3	$161.49	4.424%	$168.6343	$168.63	$168.65	$168.60
Purchase #4	$131.42	8.562%	$142.6722	$142.67	$142.65	$142.70
Purchase #5	$56.69	10.427%	$62.6011	$62.60	$62.60	$62.60
Purchase #6	$142.60	6.205%	$151.4483	$151.45	$151.45	$151.40
Purchase #7	$223.88	8.488%	$242.8829	$242.88	$242.90	$242.90
7 purchase totals =	$862.66		$920.4281	$920.42	$920.40	$920.40