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	$41.85	6.583%	$44.605	$44.61	$44.60	$44.60
Purchase #2	$62.44	7.360%	$67.0356	$67.04	$67.05	$67.00
Purchase #3	$89.98	4.705%	$94.2136	$94.21	$94.20	$94.20
Purchase #4	$131.56	6.118%	$139.6088	$139.61	$139.60	$139.60
Purchase #5	$177.83	3.253%	$183.6148	$183.61	$183.60	$183.60
Purchase #6	$72.79	8.680%	$79.1082	$79.11	$79.10	$79.10
Purchase #7	$124.98	5.452%	$131.7939	$131.79	$131.80	$131.80
7 purchase totals =	$701.43		$739.9799	$739.98	$739.95	$739.90