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	$149.80	11.417%	$166.9027	$166.90	$166.90	$166.90
Purchase #2	$162.41	11.314%	$180.7851	$180.79	$180.80	$180.80
Purchase #3	$111.78	12.822%	$126.1124	$126.11	$126.10	$126.10
Purchase #4	$245.58	10.273%	$270.8084	$270.81	$270.80	$270.80
Purchase #5	$163.74	13.136%	$185.2489	$185.25	$185.25	$185.20
Purchase #6	$165.56	8.159%	$179.068	$179.07	$179.05	$179.10
Purchase #7	$40.67	5.135%	$42.7584	$42.76	$42.75	$42.80
7 purchase totals =	$1,039.54		$1,151.6839	$1,151.69	$1,151.65	$1,151.70