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	$42.55	12.630%	$47.9241	$47.92	$47.90	$47.90
Purchase #2	$43.25	13.868%	$49.2479	$49.25	$49.25	$49.20
Purchase #3	$222.76	12.178%	$249.8877	$249.89	$249.90	$249.90
Purchase #4	$198.70	12.542%	$223.621	$223.62	$223.60	$223.60
Purchase #5	$155.74	10.773%	$172.5179	$172.52	$172.50	$172.50
Purchase #6	$90.42	10.429%	$99.8499	$99.85	$99.85	$99.80
Purchase #7	$85.79	12.548%	$96.5549	$96.55	$96.55	$96.60
7 purchase totals =	$839.21		$939.6034	$939.60	$939.55	$939.50