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	$134.99	12.729%	$152.1729	$152.17	$152.15	$152.20
Purchase #2	$205.77	12.616%	$231.7299	$231.73	$231.75	$231.70
Purchase #3	$96.56	4.357%	$100.7671	$100.77	$100.75	$100.80
Purchase #4	$96.52	12.719%	$108.7964	$108.80	$108.80	$108.80
Purchase #5	$53.44	4.240%	$55.7059	$55.71	$55.70	$55.70
Purchase #6	$44.79	6.121%	$47.5316	$47.53	$47.55	$47.50
Purchase #7	$123.76	3.786%	$128.4456	$128.45	$128.45	$128.40
7 purchase totals =	$755.83		$825.1494	$825.16	$825.15	$825.10