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	$101.73	13.780%	$115.7484	$115.75	$115.75	$115.70
Purchase #2	$80.58	3.693%	$83.5558	$83.56	$83.55	$83.60
Purchase #3	$217.58	4.694%	$227.7932	$227.79	$227.80	$227.80
Purchase #4	$141.67	13.848%	$161.2885	$161.29	$161.30	$161.30
Purchase #5	$127.92	8.853%	$139.2448	$139.24	$139.25	$139.20
Purchase #6	$67.79	7.199%	$72.6702	$72.67	$72.65	$72.70
Purchase #7	$110.50	11.322%	$123.0108	$123.01	$123.00	$123.00
7 purchase totals =	$847.77		$923.3117	$923.31	$923.30	$923.30