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	$32.64	3.860%	$33.8999	$33.90	$33.90	$33.90
Purchase #2	$33.74	4.330%	$35.2009	$35.20	$35.20	$35.20
Purchase #3	$76.85	12.422%	$86.3963	$86.40	$86.40	$86.40
Purchase #4	$86.48	6.253%	$91.8876	$91.89	$91.90	$91.90
Purchase #5	$68.76	4.305%	$71.7201	$71.72	$71.70	$71.70
Purchase #6	$69.94	10.666%	$77.3998	$77.40	$77.40	$77.40
Purchase #7	$207.71	13.185%	$235.0966	$235.10	$235.10	$235.10
7 purchase totals =	$576.12		$631.6012	$631.61	$631.60	$631.60