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	$17.52	6.694%	$18.6928	$18.69	$18.70	$18.70
Purchase #2	$162.66	5.599%	$171.7673	$171.77	$171.75	$171.80
Purchase #3	$178.66	6.241%	$189.8102	$189.81	$189.80	$189.80
Purchase #4	$98.77	12.632%	$111.2466	$111.25	$111.25	$111.20
Purchase #5	$218.79	9.627%	$239.8529	$239.85	$239.85	$239.90
Purchase #6	$31.82	4.275%	$33.1803	$33.18	$33.20	$33.20
Purchase #7	$141.37	11.418%	$157.5116	$157.51	$157.50	$157.50
7 purchase totals =	$849.59		$922.0617	$922.06	$922.05	$922.10