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	$185.30	9.822%	$203.5002	$203.50	$203.50	$203.50
Purchase #2	$168.50	6.757%	$179.8855	$179.89	$179.90	$179.90
Purchase #3	$162.41	10.385%	$179.2763	$179.28	$179.30	$179.30
Purchase #4	$164.91	13.284%	$186.8166	$186.82	$186.80	$186.80
Purchase #5	$159.58	3.493%	$165.1541	$165.15	$165.15	$165.20
Purchase #6	$189.63	7.475%	$203.8048	$203.80	$203.80	$203.80
Purchase #7	$50.72	9.320%	$55.4471	$55.45	$55.45	$55.40
7 purchase totals =	$1,081.05		$1,173.8846	$1,173.89	$1,173.90	$1,173.90