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	$178.50	4.642%	$186.786	$186.79	$186.80	$186.80
Purchase #2	$16.98	4.318%	$17.7132	$17.71	$17.70	$17.70
Purchase #3	$130.74	7.873%	$141.0332	$141.03	$141.05	$141.00
Purchase #4	$89.32	6.615%	$95.2285	$95.23	$95.25	$95.20
Purchase #5	$50.81	5.144%	$53.4237	$53.42	$53.40	$53.40
Purchase #6	$128.47	13.340%	$145.6079	$145.61	$145.60	$145.60
Purchase #7	$174.83	11.263%	$194.5211	$194.52	$194.50	$194.50
7 purchase totals =	$769.65		$834.3136	$834.31	$834.30	$834.20