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	$70.88	11.304%	$78.8923	$78.89	$78.90	$78.90
Purchase #2	$81.76	11.833%	$91.4347	$91.43	$91.45	$91.40
Purchase #3	$103.26	6.194%	$109.6559	$109.66	$109.65	$109.70
Purchase #4	$164.75	9.719%	$180.7621	$180.76	$180.75	$180.80
Purchase #5	$142.75	7.630%	$153.6418	$153.64	$153.65	$153.60
Purchase #6	$11.97	12.367%	$13.4503	$13.45	$13.45	$13.50
Purchase #7	$28.57	13.134%	$32.3224	$32.32	$32.30	$32.30
7 purchase totals =	$603.94		$660.1595	$660.15	$660.15	$660.20