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	$39.52	6.346%	$42.0279	$42.03	$42.05	$42.00
Purchase #2	$56.59	6.384%	$60.2027	$60.20	$60.20	$60.20
Purchase #3	$154.35	11.450%	$172.0231	$172.02	$172.00	$172.00
Purchase #4	$235.47	4.260%	$245.501	$245.50	$245.50	$245.50
Purchase #5	$176.42	4.363%	$184.1172	$184.12	$184.10	$184.10
Purchase #6	$100.28	6.565%	$106.8634	$106.86	$106.85	$106.90
Purchase #7	$119.28	7.823%	$128.6113	$128.61	$128.60	$128.60
7 purchase totals =	$881.91		$939.3466	$939.34	$939.30	$939.30