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	$104.96	11.597%	$117.1322	$117.13	$117.15	$117.10
Purchase #2	$107.40	10.488%	$118.6641	$118.66	$118.65	$118.70
Purchase #3	$81.54	11.751%	$91.1218	$91.12	$91.10	$91.10
Purchase #4	$112.89	12.807%	$127.3478	$127.35	$127.35	$127.30
Purchase #5	$33.86	10.550%	$37.4322	$37.43	$37.45	$37.40
Purchase #6	$126.65	7.769%	$136.4894	$136.49	$136.50	$136.50
Purchase #7	$150.87	3.588%	$156.2832	$156.28	$156.30	$156.30
7 purchase totals =	$718.17		$784.4707	$784.46	$784.50	$784.40