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	$122.30	5.144%	$128.5911	$128.59	$128.60	$128.60
Purchase #2	$116.88	12.673%	$131.6922	$131.69	$131.70	$131.70
Purchase #3	$229.29	9.114%	$250.1875	$250.19	$250.20	$250.20
Purchase #4	$200.73	10.275%	$221.355	$221.36	$221.35	$221.40
Purchase #5	$170.80	11.245%	$190.0065	$190.01	$190.00	$190.00
Purchase #6	$24.97	3.538%	$25.8534	$25.85	$25.85	$25.90
Purchase #7	$220.83	10.535%	$244.0944	$244.09	$244.10	$244.10
7 purchase totals =	$1,085.80		$1,191.7801	$1,191.78	$1,191.80	$1,191.90