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	$134.94	6.213%	$143.3238	$143.32	$143.30	$143.30
Purchase #2	$147.40	12.597%	$165.968	$165.97	$165.95	$166.00
Purchase #3	$19.56	9.109%	$21.3417	$21.34	$21.35	$21.30
Purchase #4	$67.37	8.114%	$72.8364	$72.84	$72.85	$72.80
Purchase #5	$5.41	5.844%	$5.7262	$5.73	$5.75	$5.70
Purchase #6	$100.76	8.119%	$108.9407	$108.94	$108.95	$108.90
Purchase #7	$135.38	12.446%	$152.2294	$152.23	$152.25	$152.20
7 purchase totals =	$610.82		$670.3662	$670.37	$670.40	$670.20