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	$104.89	9.828%	$115.1986	$115.20	$115.20	$115.20
Purchase #2	$104.39	7.856%	$112.5909	$112.59	$112.60	$112.60
Purchase #3	$58.41	11.823%	$65.3158	$65.32	$65.30	$65.30
Purchase #4	$98.81	13.183%	$111.8361	$111.84	$111.85	$111.80
Purchase #5	$218.94	8.121%	$236.7201	$236.72	$236.70	$236.70
Purchase #6	$28.51	5.659%	$30.1234	$30.12	$30.10	$30.10
Purchase #7	$55.92	6.620%	$59.6219	$59.62	$59.60	$59.60
7 purchase totals =	$669.87		$731.4068	$731.41	$731.35	$731.30