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	$129.64	11.143%	$144.0858	$144.09	$144.10	$144.10
Purchase #2	$99.50	9.543%	$108.9953	$109.00	$109.00	$109.00
Purchase #3	$223.97	12.473%	$251.9058	$251.91	$251.90	$251.90
Purchase #4	$61.56	6.492%	$65.5565	$65.56	$65.55	$65.60
Purchase #5	$177.53	4.240%	$185.0573	$185.06	$185.05	$185.10
Purchase #6	$53.47	10.767%	$59.2271	$59.23	$59.25	$59.20
Purchase #7	$145.29	13.527%	$164.9434	$164.94	$164.95	$164.90
7 purchase totals =	$890.96		$979.7712	$979.79	$979.80	$979.80