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	$144.78	6.731%	$154.5251	$154.53	$154.55	$154.50
Purchase #2	$43.53	4.395%	$45.4431	$45.44	$45.45	$45.40
Purchase #3	$195.89	11.480%	$218.3782	$218.38	$218.40	$218.40
Purchase #4	$103.56	3.424%	$107.1059	$107.11	$107.10	$107.10
Purchase #5	$28.92	10.811%	$32.0465	$32.05	$32.05	$32.00
Purchase #6	$174.79	6.193%	$185.6147	$185.61	$185.60	$185.60
Purchase #7	$89.51	12.230%	$100.4571	$100.46	$100.45	$100.50
7 purchase totals =	$780.98		$843.5706	$843.58	$843.60	$843.50