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	$45.34	10.315%	$50.0168	$50.02	$50.00	$50.00
Purchase #2	$238.89	8.237%	$258.5674	$258.57	$258.55	$258.60
Purchase #3	$162.71	3.842%	$168.9613	$168.96	$168.95	$169.00
Purchase #4	$89.72	5.744%	$94.8735	$94.87	$94.85	$94.90
Purchase #5	$214.87	6.312%	$228.4326	$228.43	$228.45	$228.40
Purchase #6	$192.97	8.799%	$209.9494	$209.95	$209.95	$209.90
Purchase #7	$50.54	7.815%	$54.4897	$54.49	$54.50	$54.50
7 purchase totals =	$995.04		$1,065.2907	$1,065.29	$1,065.25	$1,065.30