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	$238.47	11.187%	$265.1476	$265.15	$265.15	$265.10
Purchase #2	$45.68	8.133%	$49.3952	$49.40	$49.40	$49.40
Purchase #3	$86.82	12.292%	$97.4919	$97.49	$97.50	$97.50
Purchase #4	$239.42	6.606%	$255.2361	$255.24	$255.25	$255.20
Purchase #5	$55.61	6.298%	$59.1123	$59.11	$59.10	$59.10
Purchase #6	$90.75	8.367%	$98.3431	$98.34	$98.35	$98.30
Purchase #7	$169.47	6.169%	$179.9246	$179.92	$179.90	$179.90
7 purchase totals =	$926.22		$1,004.6508	$1,004.65	$1,004.65	$1,004.50