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	$107.67	10.717%	$119.209	$119.21	$119.20	$119.20
Purchase #2	$240.36	4.125%	$250.2749	$250.27	$250.25	$250.30
Purchase #3	$54.31	9.593%	$59.52	$59.52	$59.50	$59.50
Purchase #4	$204.72	7.285%	$219.6339	$219.63	$219.65	$219.60
Purchase #5	$170.96	4.836%	$179.2276	$179.23	$179.25	$179.20
Purchase #6	$194.38	6.256%	$206.5404	$206.54	$206.55	$206.50
Purchase #7	$174.30	6.249%	$185.192	$185.19	$185.20	$185.20
7 purchase totals =	$1,146.70		$1,219.5978	$1,219.59	$1,219.60	$1,219.50