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	$156.59	11.595%	$174.7466	$174.75	$174.75	$174.70
Purchase #2	$46.87	9.800%	$51.4633	$51.46	$51.45	$51.50
Purchase #3	$224.32	5.483%	$236.6195	$236.62	$236.60	$236.60
Purchase #4	$233.32	3.832%	$242.2608	$242.26	$242.25	$242.30
Purchase #5	$168.88	8.552%	$183.3226	$183.32	$183.30	$183.30
Purchase #6	$27.60	3.130%	$28.4639	$28.46	$28.45	$28.50
Purchase #7	$85.65	4.715%	$89.6884	$89.69	$89.70	$89.70
7 purchase totals =	$943.23		$1,006.5651	$1,006.56	$1,006.50	$1,006.60