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	$82.97	8.404%	$89.9428	$89.94	$89.95	$89.90
Purchase #2	$189.78	5.690%	$200.5785	$200.58	$200.60	$200.60
Purchase #3	$114.73	11.280%	$127.6715	$127.67	$127.65	$127.70
Purchase #4	$239.30	13.474%	$271.5433	$271.54	$271.55	$271.50
Purchase #5	$54.74	9.320%	$59.8418	$59.84	$59.85	$59.80
Purchase #6	$69.46	7.832%	$74.9001	$74.90	$74.90	$74.90
Purchase #7	$39.98	9.326%	$43.7085	$43.71	$43.70	$43.70
7 purchase totals =	$790.96		$868.1865	$868.18	$868.20	$868.10