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	$142.92	9.627%	$156.6789	$156.68	$156.70	$156.70
Purchase #2	$123.98	7.853%	$133.7161	$133.72	$133.70	$133.70
Purchase #3	$68.67	3.808%	$71.285	$71.29	$71.30	$71.30
Purchase #4	$174.89	3.164%	$180.4235	$180.42	$180.40	$180.40
Purchase #5	$178.33	10.374%	$196.83	$196.83	$196.85	$196.80
Purchase #6	$82.43	8.550%	$89.4778	$89.48	$89.50	$89.50
Purchase #7	$54.49	7.284%	$58.4591	$58.46	$58.45	$58.50
7 purchase totals =	$825.71		$886.8704	$886.88	$886.90	$886.90