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	$66.92	6.589%	$71.3294	$71.33	$71.35	$71.30
Purchase #2	$137.30	13.761%	$156.1939	$156.19	$156.20	$156.20
Purchase #3	$11.46	4.369%	$11.9607	$11.96	$11.95	$12.00
Purchase #4	$136.37	5.814%	$144.2986	$144.30	$144.30	$144.30
Purchase #5	$145.48	7.480%	$156.3619	$156.36	$156.35	$156.40
Purchase #6	$160.68	3.505%	$166.3118	$166.31	$166.30	$166.30
Purchase #7	$185.38	10.192%	$204.2739	$204.27	$204.25	$204.30
7 purchase totals =	$843.59		$910.7302	$910.72	$910.70	$910.80