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	$78.27	13.310%	$88.6877	$88.69	$88.70	$88.70
Purchase #2	$215.99	9.400%	$236.2931	$236.29	$236.30	$236.30
Purchase #3	$114.93	7.288%	$123.3061	$123.31	$123.30	$123.30
Purchase #4	$146.84	3.809%	$152.4331	$152.43	$152.45	$152.40
Purchase #5	$236.81	8.453%	$256.8275	$256.83	$256.85	$256.80
Purchase #6	$76.57	11.461%	$85.3457	$85.35	$85.35	$85.30
Purchase #7	$111.30	11.397%	$123.9849	$123.98	$124.00	$124.00
7 purchase totals =	$980.71		$1,066.8781	$1,066.88	$1,066.95	$1,066.80