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	$6.77	13.535%	$7.6863	$7.69	$7.70	$7.70
Purchase #2	$168.36	13.601%	$191.2586	$191.26	$191.25	$191.30
Purchase #3	$20.54	5.163%	$21.6005	$21.60	$21.60	$21.60
Purchase #4	$98.65	10.617%	$109.1237	$109.12	$109.10	$109.10
Purchase #5	$62.75	9.354%	$68.6196	$68.62	$68.60	$68.60
Purchase #6	$235.88	12.139%	$264.5135	$264.51	$264.50	$264.50
Purchase #7	$131.35	8.280%	$142.2258	$142.23	$142.25	$142.20
7 purchase totals =	$724.30		$805.0280	$805.03	$805.00	$805.00