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	$127.94	5.570%	$135.0663	$135.07	$135.05	$135.10
Purchase #2	$80.35	3.803%	$83.4057	$83.41	$83.40	$83.40
Purchase #3	$24.40	12.696%	$27.4978	$27.50	$27.50	$27.50
Purchase #4	$179.89	3.281%	$185.7922	$185.79	$185.80	$185.80
Purchase #5	$136.88	11.865%	$153.1208	$153.12	$153.10	$153.10
Purchase #6	$235.71	7.830%	$254.1661	$254.17	$254.15	$254.20
Purchase #7	$132.80	4.831%	$139.2156	$139.22	$139.20	$139.20
7 purchase totals =	$917.97		$978.2645	$978.28	$978.20	$978.30