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	$95.92	6.314%	$101.9764	$101.98	$102.00	$102.00
Purchase #2	$205.72	7.754%	$221.6715	$221.67	$221.65	$221.70
Purchase #3	$128.88	10.839%	$142.8493	$142.85	$142.85	$142.80
Purchase #4	$235.49	3.500%	$243.7322	$243.73	$243.75	$243.70
Purchase #5	$43.76	4.252%	$45.6207	$45.62	$45.60	$45.60
Purchase #6	$161.31	4.633%	$168.7835	$168.78	$168.80	$168.80
Purchase #7	$29.95	5.378%	$31.5607	$31.56	$31.55	$31.60
7 purchase totals =	$901.03		$956.1943	$956.19	$956.20	$956.20