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	$49.87	6.847%	$53.2846	$53.28	$53.30	$53.30
Purchase #2	$227.97	3.842%	$236.7286	$236.73	$236.75	$236.70
Purchase #3	$31.72	9.374%	$34.6934	$34.69	$34.70	$34.70
Purchase #4	$53.96	6.345%	$57.3838	$57.38	$57.40	$57.40
Purchase #5	$74.29	5.266%	$78.2021	$78.20	$78.20	$78.20
Purchase #6	$137.43	13.810%	$156.4091	$156.41	$156.40	$156.40
Purchase #7	$74.32	11.259%	$82.6877	$82.69	$82.70	$82.70
7 purchase totals =	$649.56		$699.3893	$699.38	$699.45	$699.40