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	$89.30	4.166%	$93.0202	$93.02	$93.00	$93.00
Purchase #2	$129.93	8.627%	$141.1391	$141.14	$141.15	$141.10
Purchase #3	$21.40	4.368%	$22.3348	$22.33	$22.35	$22.30
Purchase #4	$69.98	3.424%	$72.3761	$72.38	$72.40	$72.40
Purchase #5	$148.78	3.363%	$153.7835	$153.78	$153.80	$153.80
Purchase #6	$129.74	11.417%	$144.5524	$144.55	$144.55	$144.60
Purchase #7	$34.64	11.456%	$38.6084	$38.61	$38.60	$38.60
7 purchase totals =	$623.77		$665.8145	$665.81	$665.85	$665.80