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	$16.86	12.266%	$18.928	$18.93	$18.95	$18.90
Purchase #2	$245.86	11.746%	$274.7387	$274.74	$274.75	$274.70
Purchase #3	$174.34	3.537%	$180.5064	$180.51	$180.50	$180.50
Purchase #4	$159.71	4.214%	$166.4402	$166.44	$166.45	$166.40
Purchase #5	$16.96	6.670%	$18.0912	$18.09	$18.10	$18.10
Purchase #6	$129.43	12.771%	$145.9595	$145.96	$145.95	$146.00
Purchase #7	$229.48	11.759%	$256.4646	$256.46	$256.45	$256.50
7 purchase totals =	$972.64		$1,061.1286	$1,061.13	$1,061.15	$1,061.10