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	$171.51	4.111%	$178.5608	$178.56	$178.55	$178.60
Purchase #2	$27.48	6.310%	$29.214	$29.21	$29.20	$29.20
Purchase #3	$158.39	12.500%	$178.1888	$178.19	$178.20	$178.20
Purchase #4	$110.35	12.278%	$123.8988	$123.90	$123.90	$123.90
Purchase #5	$44.85	3.616%	$46.4718	$46.47	$46.45	$46.50
Purchase #6	$214.60	4.266%	$223.7548	$223.75	$223.75	$223.80
Purchase #7	$82.85	11.350%	$92.2535	$92.25	$92.25	$92.30
7 purchase totals =	$810.03		$872.3425	$872.33	$872.30	$872.50