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	$48.93	9.341%	$53.5006	$53.50	$53.50	$53.50
Purchase #2	$219.43	12.547%	$246.9619	$246.96	$246.95	$247.00
Purchase #3	$113.51	12.296%	$127.4672	$127.47	$127.45	$127.50
Purchase #4	$147.54	5.662%	$155.8937	$155.89	$155.90	$155.90
Purchase #5	$146.43	10.679%	$162.0673	$162.07	$162.05	$162.10
Purchase #6	$73.71	7.726%	$79.4048	$79.40	$79.40	$79.40
Purchase #7	$95.47	6.874%	$102.0326	$102.03	$102.05	$102.00
7 purchase totals =	$845.02		$927.3281	$927.32	$927.30	$927.40