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	$125.33	4.768%	$131.3057	$131.31	$131.30	$131.30
Purchase #2	$140.31	7.837%	$151.3061	$151.31	$151.30	$151.30
Purchase #3	$95.29	5.570%	$100.5977	$100.60	$100.60	$100.60
Purchase #4	$250.88	8.593%	$272.4381	$272.44	$272.45	$272.40
Purchase #5	$250.62	9.276%	$273.8675	$273.87	$273.85	$273.90
Purchase #6	$131.95	10.473%	$145.7691	$145.77	$145.75	$145.80
Purchase #7	$189.76	12.188%	$212.8879	$212.89	$212.90	$212.90
7 purchase totals =	$1,184.14		$1,288.1721	$1,288.19	$1,288.15	$1,288.20