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	$149.52	9.787%	$164.1535	$164.15	$164.15	$164.20
Purchase #2	$39.98	6.458%	$42.5619	$42.56	$42.55	$42.60
Purchase #3	$141.96	6.747%	$151.538	$151.54	$151.55	$151.50
Purchase #4	$149.64	12.436%	$168.2492	$168.25	$168.25	$168.20
Purchase #5	$52.56	3.236%	$54.2608	$54.26	$54.25	$54.30
Purchase #6	$56.38	9.200%	$61.567	$61.57	$61.55	$61.60
Purchase #7	$5.56	10.491%	$6.1433	$6.14	$6.15	$6.10
7 purchase totals =	$595.60		$648.4737	$648.47	$648.45	$648.50