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	$51.99	6.173%	$55.1993	$55.20	$55.20	$55.20
Purchase #2	$195.59	12.336%	$219.718	$219.72	$219.70	$219.70
Purchase #3	$129.96	13.454%	$147.4448	$147.44	$147.45	$147.40
Purchase #4	$79.50	13.301%	$90.0743	$90.07	$90.05	$90.10
Purchase #5	$31.31	11.429%	$34.8884	$34.89	$34.90	$34.90
Purchase #6	$135.27	5.127%	$142.2053	$142.21	$142.20	$142.20
Purchase #7	$231.47	10.577%	$255.9526	$255.95	$255.95	$256.00
7 purchase totals =	$855.09		$945.4827	$945.48	$945.45	$945.50