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	$155.80	4.168%	$162.2937	$162.29	$162.30	$162.30
Purchase #2	$154.25	10.760%	$170.8473	$170.85	$170.85	$170.80
Purchase #3	$75.73	3.446%	$78.3397	$78.34	$78.35	$78.30
Purchase #4	$23.49	3.580%	$24.3309	$24.33	$24.35	$24.30
Purchase #5	$148.56	13.632%	$168.8117	$168.81	$168.80	$168.80
Purchase #6	$249.42	11.709%	$278.6246	$278.62	$278.60	$278.60
Purchase #7	$238.97	12.490%	$268.8174	$268.82	$268.80	$268.80
7 purchase totals =	$1,046.22		$1,152.0653	$1,152.06	$1,152.05	$1,151.90