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	$73.52	6.804%	$78.5223	$78.52	$78.50	$78.50
Purchase #2	$25.51	10.729%	$28.247	$28.25	$28.25	$28.20
Purchase #3	$158.57	8.669%	$172.3164	$172.32	$172.30	$172.30
Purchase #4	$46.75	9.800%	$51.3315	$51.33	$51.35	$51.30
Purchase #5	$24.69	5.556%	$26.0618	$26.06	$26.05	$26.10
Purchase #6	$191.38	10.230%	$210.9582	$210.96	$210.95	$211.00
Purchase #7	$38.27	5.553%	$40.3951	$40.40	$40.40	$40.40
7 purchase totals =	$558.69		$607.8323	$607.84	$607.80	$607.80