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	$67.40	5.124%	$70.8536	$70.85	$70.85	$70.90
Purchase #2	$185.96	6.768%	$198.5458	$198.55	$198.55	$198.50
Purchase #3	$182.34	7.621%	$196.2361	$196.24	$196.25	$196.20
Purchase #4	$140.76	12.691%	$158.6239	$158.62	$158.60	$158.60
Purchase #5	$105.34	7.129%	$112.8497	$112.85	$112.85	$112.80
Purchase #6	$48.51	12.320%	$54.4864	$54.49	$54.50	$54.50
Purchase #7	$107.55	4.413%	$112.2962	$112.30	$112.30	$112.30
7 purchase totals =	$837.86		$903.8917	$903.90	$903.90	$903.80