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	$96.83	3.195%	$99.9237	$99.92	$99.90	$99.90
Purchase #2	$247.57	5.361%	$260.8422	$260.84	$260.85	$260.80
Purchase #3	$190.48	10.184%	$209.8785	$209.88	$209.90	$209.90
Purchase #4	$47.36	7.693%	$51.0034	$51.00	$51.00	$51.00
Purchase #5	$104.62	6.436%	$111.3533	$111.35	$111.35	$111.40
Purchase #6	$228.59	12.458%	$257.0677	$257.07	$257.05	$257.10
Purchase #7	$135.66	12.613%	$152.7708	$152.77	$152.75	$152.80
7 purchase totals =	$1,051.11		$1,142.8396	$1,142.83	$1,142.80	$1,142.90