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	$134.26	8.751%	$146.0091	$146.01	$146.00	$146.00
Purchase #2	$152.56	7.581%	$164.1256	$164.13	$164.15	$164.10
Purchase #3	$81.37	10.521%	$89.9309	$89.93	$89.95	$89.90
Purchase #4	$113.80	11.547%	$126.9405	$126.94	$126.95	$126.90
Purchase #5	$53.74	9.114%	$58.6379	$58.64	$58.65	$58.60
Purchase #6	$37.46	12.393%	$42.1024	$42.10	$42.10	$42.10
Purchase #7	$38.60	10.686%	$42.7248	$42.72	$42.70	$42.70
7 purchase totals =	$611.79		$670.4712	$670.47	$670.50	$670.30