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	$241.61	12.330%	$271.4005	$271.40	$271.40	$271.40
Purchase #2	$55.85	9.752%	$61.2965	$61.30	$61.30	$61.30
Purchase #3	$48.61	4.475%	$50.7853	$50.79	$50.80	$50.80
Purchase #4	$31.56	6.304%	$33.5495	$33.55	$33.55	$33.50
Purchase #5	$85.91	11.675%	$95.94	$95.94	$95.95	$95.90
Purchase #6	$18.62	12.460%	$20.9401	$20.94	$20.95	$20.90
Purchase #7	$30.40	7.102%	$32.559	$32.56	$32.55	$32.60
7 purchase totals =	$512.56		$566.4709	$566.48	$566.50	$566.40