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	$246.42	7.214%	$264.1967	$264.20	$264.20	$264.20
Purchase #2	$174.28	12.680%	$196.3787	$196.38	$196.40	$196.40
Purchase #3	$89.67	9.528%	$98.2138	$98.21	$98.20	$98.20
Purchase #4	$113.99	11.706%	$127.3337	$127.33	$127.35	$127.30
Purchase #5	$21.64	11.580%	$24.1459	$24.15	$24.15	$24.10
Purchase #6	$92.59	13.410%	$105.0063	$105.01	$105.00	$105.00
Purchase #7	$141.56	4.572%	$148.0321	$148.03	$148.05	$148.00
7 purchase totals =	$880.15		$963.3072	$963.31	$963.35	$963.20