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	$14.86	9.832%	$16.321	$16.32	$16.30	$16.30
Purchase #2	$143.37	9.319%	$156.7307	$156.73	$156.75	$156.70
Purchase #3	$123.47	13.647%	$140.32	$140.32	$140.30	$140.30
Purchase #4	$39.98	6.452%	$42.5595	$42.56	$42.55	$42.60
Purchase #5	$78.93	12.598%	$88.8736	$88.87	$88.85	$88.90
Purchase #6	$152.50	4.817%	$159.8459	$159.85	$159.85	$159.80
Purchase #7	$72.71	10.670%	$80.4682	$80.47	$80.45	$80.50
7 purchase totals =	$625.82		$685.1189	$685.12	$685.05	$685.10