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	$56.89	11.588%	$63.4824	$63.48	$63.50	$63.50
Purchase #2	$239.69	3.440%	$247.9353	$247.94	$247.95	$247.90
Purchase #3	$190.75	9.760%	$209.3672	$209.37	$209.35	$209.40
Purchase #4	$105.30	6.309%	$111.9434	$111.94	$111.95	$111.90
Purchase #5	$180.86	6.665%	$192.9143	$192.91	$192.90	$192.90
Purchase #6	$85.48	11.702%	$95.4829	$95.48	$95.50	$95.50
Purchase #7	$148.50	5.530%	$156.7121	$156.71	$156.70	$156.70
7 purchase totals =	$1,007.47		$1,077.8376	$1,077.83	$1,077.85	$1,077.80