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	$37.73	8.411%	$40.9035	$40.90	$40.90	$40.90
Purchase #2	$34.33	9.472%	$37.5817	$37.58	$37.60	$37.60
Purchase #3	$222.42	8.180%	$240.614	$240.61	$240.60	$240.60
Purchase #4	$22.33	13.135%	$25.263	$25.26	$25.25	$25.30
Purchase #5	$217.82	5.373%	$229.5235	$229.52	$229.50	$229.50
Purchase #6	$21.44	13.537%	$24.3423	$24.34	$24.35	$24.30
Purchase #7	$5.85	4.449%	$6.1103	$6.11	$6.10	$6.10
7 purchase totals =	$561.92		$604.3383	$604.32	$604.30	$604.30