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	$5.63	4.686%	$5.8938	$5.89	$5.90	$5.90
Purchase #2	$209.43	9.522%	$229.3719	$229.37	$229.35	$229.40
Purchase #3	$126.51	3.453%	$130.8784	$130.88	$130.90	$130.90
Purchase #4	$162.92	5.309%	$171.5694	$171.57	$171.55	$171.60
Purchase #5	$43.55	4.111%	$45.3403	$45.34	$45.35	$45.30
Purchase #6	$118.84	12.830%	$134.0872	$134.09	$134.10	$134.10
Purchase #7	$233.73	4.829%	$245.0168	$245.02	$245.00	$245.00
7 purchase totals =	$900.61		$962.1578	$962.16	$962.15	$962.20