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	$93.99	5.859%	$99.4969	$99.50	$99.50	$99.50
Purchase #2	$79.48	11.473%	$88.5987	$88.60	$88.60	$88.60
Purchase #3	$195.62	7.787%	$210.8529	$210.85	$210.85	$210.90
Purchase #4	$226.83	7.338%	$243.4748	$243.47	$243.45	$243.50
Purchase #5	$62.36	5.177%	$65.5884	$65.59	$65.60	$65.60
Purchase #6	$99.59	4.588%	$104.1592	$104.16	$104.15	$104.20
Purchase #7	$102.94	6.525%	$109.6568	$109.66	$109.65	$109.70
7 purchase totals =	$860.81		$921.8277	$921.83	$921.80	$922.00