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	$100.45	8.624%	$109.1128	$109.11	$109.10	$109.10
Purchase #2	$20.72	8.784%	$22.54	$22.54	$22.55	$22.50
Purchase #3	$198.40	5.291%	$208.8973	$208.90	$208.90	$208.90
Purchase #4	$206.91	8.136%	$223.7442	$223.74	$223.75	$223.70
Purchase #5	$199.30	3.641%	$206.5565	$206.56	$206.55	$206.60
Purchase #6	$19.86	3.795%	$20.6137	$20.61	$20.60	$20.60
Purchase #7	$124.69	12.227%	$139.9358	$139.94	$139.95	$139.90
7 purchase totals =	$870.33		$931.4003	$931.40	$931.40	$931.30