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	$109.30	13.352%	$123.8937	$123.89	$123.90	$123.90
Purchase #2	$155.65	8.148%	$168.3324	$168.33	$168.35	$168.30
Purchase #3	$208.52	13.233%	$236.1135	$236.11	$236.10	$236.10
Purchase #4	$124.50	3.254%	$128.5512	$128.55	$128.55	$128.60
Purchase #5	$154.89	6.380%	$164.772	$164.77	$164.75	$164.80
Purchase #6	$219.86	4.809%	$230.4331	$230.43	$230.45	$230.40
Purchase #7	$58.66	5.239%	$61.7332	$61.73	$61.75	$61.70
7 purchase totals =	$1,031.38		$1,113.8291	$1,113.81	$1,113.85	$1,113.80