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	$29.33	6.459%	$31.2244	$31.22	$31.20	$31.20
Purchase #2	$122.58	7.548%	$131.8323	$131.83	$131.85	$131.80
Purchase #3	$48.37	6.345%	$51.4391	$51.44	$51.45	$51.40
Purchase #4	$160.82	3.856%	$167.0212	$167.02	$167.00	$167.00
Purchase #5	$73.68	12.150%	$82.6321	$82.63	$82.65	$82.60
Purchase #6	$36.70	7.262%	$39.3652	$39.37	$39.35	$39.40
Purchase #7	$236.73	3.413%	$244.8096	$244.81	$244.80	$244.80
7 purchase totals =	$708.21		$748.3239	$748.32	$748.30	$748.20