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	$235.90	3.107%	$243.2294	$243.23	$243.25	$243.20
Purchase #2	$75.32	9.663%	$82.5982	$82.60	$82.60	$82.60
Purchase #3	$64.65	10.737%	$71.5915	$71.59	$71.60	$71.60
Purchase #4	$91.45	4.522%	$95.5854	$95.59	$95.60	$95.60
Purchase #5	$114.55	11.860%	$128.1356	$128.14	$128.15	$128.10
Purchase #6	$130.99	12.637%	$147.5432	$147.54	$147.55	$147.50
Purchase #7	$115.57	12.238%	$129.7135	$129.71	$129.70	$129.70
7 purchase totals =	$828.43		$898.3968	$898.40	$898.45	$898.30