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	$133.48	6.223%	$141.7865	$141.79	$141.80	$141.80
Purchase #2	$132.75	6.501%	$141.3801	$141.38	$141.40	$141.40
Purchase #3	$82.29	8.806%	$89.5365	$89.54	$89.55	$89.50
Purchase #4	$10.33	7.259%	$11.0799	$11.08	$11.10	$11.10
Purchase #5	$17.59	13.805%	$20.0183	$20.02	$20.00	$20.00
Purchase #6	$36.55	7.196%	$39.1801	$39.18	$39.20	$39.20
Purchase #7	$73.92	8.286%	$80.045	$80.05	$80.05	$80.00
7 purchase totals =	$486.91		$523.0264	$523.04	$523.10	$523.00