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	$228.86	8.743%	$248.8692	$248.87	$248.85	$248.90
Purchase #2	$25.30	7.554%	$27.2112	$27.21	$27.20	$27.20
Purchase #3	$90.71	8.630%	$98.5383	$98.54	$98.55	$98.50
Purchase #4	$212.46	8.308%	$230.1112	$230.11	$230.10	$230.10
Purchase #5	$10.27	13.296%	$11.6355	$11.64	$11.65	$11.60
Purchase #6	$83.91	7.842%	$90.4902	$90.49	$90.50	$90.50
Purchase #7	$48.85	8.851%	$53.1737	$53.17	$53.15	$53.20
7 purchase totals =	$700.36		$760.0293	$760.03	$760.00	$760.00