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	$39.56	7.347%	$42.4665	$42.47	$42.45	$42.50
Purchase #2	$120.63	9.719%	$132.354	$132.35	$132.35	$132.40
Purchase #3	$102.71	8.576%	$111.5184	$111.52	$111.50	$111.50
Purchase #4	$72.55	3.413%	$75.0261	$75.03	$75.05	$75.00
Purchase #5	$61.48	6.818%	$65.6717	$65.67	$65.65	$65.70
Purchase #6	$148.72	9.499%	$162.8469	$162.85	$162.85	$162.80
Purchase #7	$30.69	7.625%	$33.0301	$33.03	$33.05	$33.00
7 purchase totals =	$576.34		$622.9137	$622.92	$622.90	$622.90