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	$232.30	13.472%	$263.5955	$263.60	$263.60	$263.60
Purchase #2	$50.72	11.728%	$56.6684	$56.67	$56.65	$56.70
Purchase #3	$25.43	12.796%	$28.684	$28.68	$28.70	$28.70
Purchase #4	$227.70	11.459%	$253.7921	$253.79	$253.80	$253.80
Purchase #5	$151.64	4.738%	$158.8247	$158.82	$158.80	$158.80
Purchase #6	$79.61	4.782%	$83.417	$83.42	$83.40	$83.40
Purchase #7	$32.28	4.107%	$33.6057	$33.61	$33.60	$33.60
7 purchase totals =	$799.68		$878.5874	$878.59	$878.55	$878.60