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	$34.25	9.671%	$37.5623	$37.56	$37.55	$37.60
Purchase #2	$99.36	10.119%	$109.4142	$109.41	$109.40	$109.40
Purchase #3	$196.94	6.637%	$210.0109	$210.01	$210.00	$210.00
Purchase #4	$128.38	3.476%	$132.8425	$132.84	$132.85	$132.80
Purchase #5	$244.73	10.196%	$269.6827	$269.68	$269.70	$269.70
Purchase #6	$174.87	3.692%	$181.3262	$181.33	$181.35	$181.30
Purchase #7	$139.72	4.445%	$145.9306	$145.93	$145.95	$145.90
7 purchase totals =	$1,018.25		$1,086.7694	$1,086.76	$1,086.80	$1,086.70