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	$105.55	4.158%	$109.9388	$109.94	$109.95	$109.90
Purchase #2	$157.71	5.581%	$166.5118	$166.51	$166.50	$166.50
Purchase #3	$250.59	13.108%	$283.4373	$283.44	$283.45	$283.40
Purchase #4	$30.64	8.156%	$33.139	$33.14	$33.15	$33.10
Purchase #5	$181.89	13.350%	$206.1723	$206.17	$206.15	$206.20
Purchase #6	$81.69	9.203%	$89.2079	$89.21	$89.20	$89.20
Purchase #7	$72.91	13.108%	$82.467	$82.47	$82.45	$82.50
7 purchase totals =	$880.98		$970.8741	$970.88	$970.85	$970.80