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	$52.57	11.580%	$58.6576	$58.66	$58.65	$58.70
Purchase #2	$85.62	12.345%	$96.1898	$96.19	$96.20	$96.20
Purchase #3	$49.88	13.507%	$56.6173	$56.62	$56.60	$56.60
Purchase #4	$38.31	13.110%	$43.3324	$43.33	$43.35	$43.30
Purchase #5	$84.80	7.537%	$91.1914	$91.19	$91.20	$91.20
Purchase #6	$69.69	9.860%	$76.5614	$76.56	$76.55	$76.60
Purchase #7	$70.95	11.231%	$78.9184	$78.92	$78.90	$78.90
7 purchase totals =	$451.82		$501.4683	$501.47	$501.45	$501.50