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	$96.96	3.658%	$100.5068	$100.51	$100.50	$100.50
Purchase #2	$47.85	10.348%	$52.8015	$52.80	$52.80	$52.80
Purchase #3	$34.32	10.287%	$37.8505	$37.85	$37.85	$37.90
Purchase #4	$80.55	7.721%	$86.7693	$86.77	$86.75	$86.80
Purchase #5	$121.79	5.539%	$128.5359	$128.54	$128.55	$128.50
Purchase #6	$165.29	3.625%	$171.2818	$171.28	$171.30	$171.30
Purchase #7	$69.62	6.223%	$73.9525	$73.95	$73.95	$74.00
7 purchase totals =	$616.38		$651.6983	$651.70	$651.70	$651.80