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	$109.40	7.130%	$117.2002	$117.20	$117.20	$117.20
Purchase #2	$215.65	12.588%	$242.796	$242.80	$242.80	$242.80
Purchase #3	$11.27	9.674%	$12.3603	$12.36	$12.35	$12.40
Purchase #4	$52.66	12.689%	$59.342	$59.34	$59.35	$59.30
Purchase #5	$131.88	6.720%	$140.7423	$140.74	$140.75	$140.70
Purchase #6	$45.29	11.262%	$50.3906	$50.39	$50.40	$50.40
Purchase #7	$80.33	4.106%	$83.6283	$83.63	$83.65	$83.60
7 purchase totals =	$646.48		$706.4597	$706.46	$706.50	$706.40