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	$157.74	6.592%	$168.1382	$168.14	$168.15	$168.10
Purchase #2	$79.86	11.537%	$89.0734	$89.07	$89.05	$89.10
Purchase #3	$14.29	3.483%	$14.7877	$14.79	$14.80	$14.80
Purchase #4	$17.80	4.773%	$18.6496	$18.65	$18.65	$18.60
Purchase #5	$67.32	13.632%	$76.4971	$76.50	$76.50	$76.50
Purchase #6	$166.41	8.506%	$180.5648	$180.56	$180.55	$180.60
Purchase #7	$12.69	3.661%	$13.1546	$13.15	$13.15	$13.20
7 purchase totals =	$516.11		$560.8654	$560.86	$560.85	$560.90