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	$39.77	6.139%	$42.2115	$42.21	$42.20	$42.20
Purchase #2	$49.77	7.371%	$53.4385	$53.44	$53.45	$53.40
Purchase #3	$159.90	8.542%	$173.5587	$173.56	$173.55	$173.60
Purchase #4	$211.94	7.566%	$227.9754	$227.98	$228.00	$228.00
Purchase #5	$131.98	7.789%	$142.2599	$142.26	$142.25	$142.30
Purchase #6	$127.94	12.428%	$143.8404	$143.84	$143.85	$143.80
Purchase #7	$146.66	9.764%	$160.9799	$160.98	$161.00	$161.00
7 purchase totals =	$867.96		$944.2643	$944.27	$944.30	$944.30