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	$64.42	12.241%	$72.3057	$72.31	$72.30	$72.30
Purchase #2	$58.84	12.814%	$66.3798	$66.38	$66.40	$66.40
Purchase #3	$35.86	9.836%	$39.3872	$39.39	$39.40	$39.40
Purchase #4	$141.63	6.566%	$150.9294	$150.93	$150.95	$150.90
Purchase #5	$172.71	10.538%	$190.9102	$190.91	$190.90	$190.90
Purchase #6	$109.64	4.323%	$114.3797	$114.38	$114.40	$114.40
Purchase #7	$213.32	11.268%	$237.3569	$237.36	$237.35	$237.40
7 purchase totals =	$796.42		$871.6489	$871.66	$871.70	$871.70