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	$162.77	10.606%	$180.0334	$180.03	$180.05	$180.00
Purchase #2	$158.98	5.833%	$168.2533	$168.25	$168.25	$168.30
Purchase #3	$171.33	9.819%	$188.1529	$188.15	$188.15	$188.20
Purchase #4	$47.64	10.182%	$52.4907	$52.49	$52.50	$52.50
Purchase #5	$49.75	8.575%	$54.0161	$54.02	$54.00	$54.00
Purchase #6	$33.88	9.205%	$36.9987	$37.00	$37.00	$37.00
Purchase #7	$159.56	7.745%	$171.9179	$171.92	$171.90	$171.90
7 purchase totals =	$783.91		$851.8630	$851.86	$851.85	$851.90