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	$141.29	3.500%	$146.2352	$146.24	$146.25	$146.20
Purchase #2	$134.69	11.634%	$150.3598	$150.36	$150.35	$150.40
Purchase #3	$40.75	6.441%	$43.3747	$43.37	$43.35	$43.40
Purchase #4	$123.51	13.738%	$140.4778	$140.48	$140.50	$140.50
Purchase #5	$209.29	11.535%	$233.4316	$233.43	$233.45	$233.40
Purchase #6	$31.99	9.781%	$35.1189	$35.12	$35.10	$35.10
Purchase #7	$44.85	12.408%	$50.415	$50.42	$50.40	$50.40
7 purchase totals =	$726.37		$799.4130	$799.42	$799.40	$799.40