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	$183.29	8.499%	$198.8678	$198.87	$198.85	$198.90
Purchase #2	$185.30	6.165%	$196.7237	$196.72	$196.70	$196.70
Purchase #3	$107.67	10.514%	$118.9904	$118.99	$119.00	$119.00
Purchase #4	$90.45	5.658%	$95.5677	$95.57	$95.55	$95.60
Purchase #5	$223.55	4.202%	$232.9436	$232.94	$232.95	$232.90
Purchase #6	$100.52	9.296%	$109.8643	$109.86	$109.85	$109.90
Purchase #7	$201.68	12.731%	$227.3559	$227.36	$227.35	$227.40
7 purchase totals =	$1,092.46		$1,180.3134	$1,180.31	$1,180.25	$1,180.40