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	$20.56	9.618%	$22.5375	$22.54	$22.55	$22.50
Purchase #2	$12.39	10.102%	$13.6416	$13.64	$13.65	$13.60
Purchase #3	$135.57	12.215%	$152.1299	$152.13	$152.15	$152.10
Purchase #4	$44.45	7.764%	$47.9011	$47.90	$47.90	$47.90
Purchase #5	$81.42	10.262%	$89.7753	$89.78	$89.80	$89.80
Purchase #6	$59.73	7.820%	$64.4009	$64.40	$64.40	$64.40
Purchase #7	$244.25	8.431%	$264.8427	$264.84	$264.85	$264.80
7 purchase totals =	$598.37		$655.2290	$655.23	$655.30	$655.10