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	$40.59	5.297%	$42.7401	$42.74	$42.75	$42.70
Purchase #2	$7.35	7.619%	$7.91	$7.91	$7.90	$7.90
Purchase #3	$229.93	5.590%	$242.7831	$242.78	$242.80	$242.80
Purchase #4	$25.97	4.549%	$27.1514	$27.15	$27.15	$27.20
Purchase #5	$83.36	11.110%	$92.6213	$92.62	$92.60	$92.60
Purchase #6	$83.81	6.172%	$88.9828	$88.98	$89.00	$89.00
Purchase #7	$16.83	7.522%	$18.096	$18.10	$18.10	$18.10
7 purchase totals =	$487.84		$520.2847	$520.28	$520.30	$520.30