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	$164.49	3.413%	$170.104	$170.10	$170.10	$170.10
Purchase #2	$62.59	11.477%	$69.7735	$69.77	$69.75	$69.80
Purchase #3	$37.51	12.822%	$42.3195	$42.32	$42.30	$42.30
Purchase #4	$52.69	7.198%	$56.4826	$56.48	$56.50	$56.50
Purchase #5	$49.51	5.763%	$52.3633	$52.36	$52.35	$52.40
Purchase #6	$156.98	5.631%	$165.8195	$165.82	$165.80	$165.80
Purchase #7	$82.58	5.177%	$86.8552	$86.86	$86.85	$86.90
7 purchase totals =	$606.35		$643.7176	$643.71	$643.65	$643.80