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	$149.38	3.352%	$154.3872	$154.39	$154.40	$154.40
Purchase #2	$161.97	3.633%	$167.8544	$167.85	$167.85	$167.90
Purchase #3	$110.69	4.199%	$115.3379	$115.34	$115.35	$115.30
Purchase #4	$105.29	13.418%	$119.4178	$119.42	$119.40	$119.40
Purchase #5	$172.75	3.578%	$178.931	$178.93	$178.95	$178.90
Purchase #6	$83.50	7.321%	$89.613	$89.61	$89.60	$89.60
Purchase #7	$50.61	8.814%	$55.0708	$55.07	$55.05	$55.10
7 purchase totals =	$834.19		$880.6121	$880.61	$880.60	$880.60