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	$98.35	9.189%	$107.3874	$107.39	$107.40	$107.40
Purchase #2	$139.26	4.498%	$145.5239	$145.52	$145.50	$145.50
Purchase #3	$94.29	9.417%	$103.1693	$103.17	$103.15	$103.20
Purchase #4	$100.93	4.154%	$105.1226	$105.12	$105.10	$105.10
Purchase #5	$113.36	10.738%	$125.5326	$125.53	$125.55	$125.50
Purchase #6	$114.72	5.268%	$120.7634	$120.76	$120.75	$120.80
Purchase #7	$75.89	12.703%	$85.5303	$85.53	$85.55	$85.50
7 purchase totals =	$736.80		$793.0295	$793.02	$793.00	$793.00