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	$153.39	9.237%	$167.5586	$167.56	$167.55	$167.60
Purchase #2	$144.88	13.814%	$164.8937	$164.89	$164.90	$164.90
Purchase #3	$26.64	7.745%	$28.7033	$28.70	$28.70	$28.70
Purchase #4	$101.79	12.745%	$114.7631	$114.76	$114.75	$114.80
Purchase #5	$95.55	5.222%	$100.5396	$100.54	$100.55	$100.50
Purchase #6	$134.55	5.341%	$141.7363	$141.74	$141.75	$141.70
Purchase #7	$123.87	3.820%	$128.6018	$128.60	$128.60	$128.60
7 purchase totals =	$780.67		$846.7964	$846.79	$846.80	$846.80