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	$114.84	13.641%	$130.5053	$130.51	$130.50	$130.50
Purchase #2	$135.26	11.792%	$151.2099	$151.21	$151.20	$151.20
Purchase #3	$72.30	11.298%	$80.4685	$80.47	$80.45	$80.50
Purchase #4	$52.59	6.181%	$55.8406	$55.84	$55.85	$55.80
Purchase #5	$25.34	10.872%	$28.095	$28.10	$28.10	$28.10
Purchase #6	$101.69	10.658%	$112.5281	$112.53	$112.55	$112.50
Purchase #7	$10.55	12.225%	$11.8397	$11.84	$11.85	$11.80
7 purchase totals =	$512.57		$570.4871	$570.50	$570.50	$570.40