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	$75.71	6.796%	$80.8553	$80.86	$80.85	$80.90
Purchase #2	$138.90	5.721%	$146.8465	$146.85	$146.85	$146.80
Purchase #3	$151.44	9.446%	$165.745	$165.75	$165.75	$165.70
Purchase #4	$148.84	8.146%	$160.9645	$160.96	$160.95	$161.00
Purchase #5	$165.45	12.278%	$185.764	$185.76	$185.75	$185.80
Purchase #6	$112.34	6.546%	$119.6938	$119.69	$119.70	$119.70
Purchase #7	$145.26	7.113%	$155.5923	$155.59	$155.60	$155.60
7 purchase totals =	$937.94		$1,015.4614	$1,015.46	$1,015.45	$1,015.50