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	$85.45	5.191%	$89.8857	$89.89	$89.90	$89.90
Purchase #2	$55.66	13.446%	$63.144	$63.14	$63.15	$63.10
Purchase #3	$105.57	13.382%	$119.6974	$119.70	$119.70	$119.70
Purchase #4	$55.33	3.301%	$57.1564	$57.16	$57.15	$57.20
Purchase #5	$176.48	9.817%	$193.805	$193.81	$193.80	$193.80
Purchase #6	$67.57	4.264%	$70.4512	$70.45	$70.45	$70.50
Purchase #7	$91.43	5.518%	$96.4751	$96.48	$96.50	$96.50
7 purchase totals =	$637.49		$690.6148	$690.63	$690.65	$690.70