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	$79.32	4.146%	$82.6086	$82.61	$82.60	$82.60
Purchase #2	$122.87	7.200%	$131.7166	$131.72	$131.70	$131.70
Purchase #3	$42.60	5.676%	$45.018	$45.02	$45.00	$45.00
Purchase #4	$79.77	12.317%	$89.5953	$89.60	$89.60	$89.60
Purchase #5	$242.28	12.114%	$271.6298	$271.63	$271.65	$271.60
Purchase #6	$68.96	5.693%	$72.8859	$72.89	$72.90	$72.90
Purchase #7	$93.47	11.211%	$103.9489	$103.95	$103.95	$103.90
7 purchase totals =	$729.27		$797.4031	$797.42	$797.40	$797.30