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	$238.74	13.146%	$270.1248	$270.12	$270.10	$270.10
Purchase #2	$158.81	6.275%	$168.7753	$168.78	$168.80	$168.80
Purchase #3	$97.34	4.199%	$101.4273	$101.43	$101.45	$101.40
Purchase #4	$85.40	12.701%	$96.2467	$96.25	$96.25	$96.20
Purchase #5	$72.56	8.407%	$78.6601	$78.66	$78.65	$78.70
Purchase #6	$241.91	3.345%	$250.0019	$250.00	$250.00	$250.00
Purchase #7	$69.44	13.587%	$78.8748	$78.87	$78.85	$78.90
7 purchase totals =	$964.20		$1,044.1109	$1,044.11	$1,044.10	$1,044.10