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	$125.73	11.142%	$139.7388	$139.74	$139.75	$139.70
Purchase #2	$108.59	3.793%	$112.7088	$112.71	$112.70	$112.70
Purchase #3	$128.29	11.380%	$142.8894	$142.89	$142.90	$142.90
Purchase #4	$213.98	13.335%	$242.5142	$242.51	$242.50	$242.50
Purchase #5	$143.79	8.626%	$156.1933	$156.19	$156.20	$156.20
Purchase #6	$27.40	10.460%	$30.266	$30.27	$30.25	$30.30
Purchase #7	$219.56	12.639%	$247.3102	$247.31	$247.30	$247.30
7 purchase totals =	$967.34		$1,071.6207	$1,071.62	$1,071.60	$1,071.60