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	$94.29	6.378%	$100.3038	$100.30	$100.30	$100.30
Purchase #2	$121.46	5.352%	$127.9605	$127.96	$127.95	$128.00
Purchase #3	$137.46	3.674%	$142.5103	$142.51	$142.50	$142.50
Purchase #4	$200.33	3.196%	$206.7325	$206.73	$206.75	$206.70
Purchase #5	$107.52	8.178%	$116.313	$116.31	$116.30	$116.30
Purchase #6	$186.91	6.121%	$198.3508	$198.35	$198.35	$198.40
Purchase #7	$41.59	11.393%	$46.3283	$46.33	$46.35	$46.30
7 purchase totals =	$889.56		$938.4992	$938.49	$938.50	$938.50