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	$17.92	5.412%	$18.8898	$18.89	$18.90	$18.90
Purchase #2	$246.98	10.534%	$272.9969	$273.00	$273.00	$273.00
Purchase #3	$68.37	5.185%	$71.915	$71.92	$71.90	$71.90
Purchase #4	$88.71	3.251%	$91.594	$91.59	$91.60	$91.60
Purchase #5	$142.79	6.502%	$152.0742	$152.07	$152.05	$152.10
Purchase #6	$119.63	10.175%	$131.8024	$131.80	$131.80	$131.80
Purchase #7	$137.78	5.827%	$145.8084	$145.81	$145.80	$145.80
7 purchase totals =	$822.18		$885.0807	$885.08	$885.05	$885.10