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	$66.81	10.569%	$73.8711	$73.87	$73.85	$73.90
Purchase #2	$113.62	5.770%	$120.1759	$120.18	$120.20	$120.20
Purchase #3	$103.69	5.338%	$109.225	$109.23	$109.25	$109.20
Purchase #4	$235.73	11.524%	$262.8955	$262.90	$262.90	$262.90
Purchase #5	$89.82	10.755%	$99.4801	$99.48	$99.50	$99.50
Purchase #6	$194.83	7.335%	$209.1208	$209.12	$209.10	$209.10
Purchase #7	$103.39	11.197%	$114.9666	$114.97	$114.95	$115.00
7 purchase totals =	$907.89		$989.7350	$989.75	$989.75	$989.80