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	$142.39	4.150%	$148.2992	$148.30	$148.30	$148.30
Purchase #2	$226.29	10.482%	$250.0097	$250.01	$250.00	$250.00
Purchase #3	$111.38	6.438%	$118.5506	$118.55	$118.55	$118.60
Purchase #4	$178.27	11.841%	$199.379	$199.38	$199.40	$199.40
Purchase #5	$236.64	5.621%	$249.9415	$249.94	$249.95	$249.90
Purchase #6	$165.90	6.251%	$176.2704	$176.27	$176.25	$176.30
Purchase #7	$167.30	7.558%	$179.9445	$179.94	$179.95	$179.90
7 purchase totals =	$1,228.17		$1,322.3949	$1,322.39	$1,322.40	$1,322.40