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	$246.40	9.137%	$268.9136	$268.91	$268.90	$268.90
Purchase #2	$225.59	8.384%	$244.5035	$244.50	$244.50	$244.50
Purchase #3	$233.98	12.150%	$262.4086	$262.41	$262.40	$262.40
Purchase #4	$131.32	12.525%	$147.7678	$147.77	$147.75	$147.80
Purchase #5	$65.56	6.683%	$69.9414	$69.94	$69.95	$69.90
Purchase #6	$42.32	8.343%	$45.8508	$45.85	$45.85	$45.90
Purchase #7	$91.73	10.636%	$101.4864	$101.49	$101.50	$101.50
7 purchase totals =	$1,036.90		$1,140.8721	$1,140.87	$1,140.85	$1,140.90