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	$87.95	3.377%	$90.9201	$90.92	$90.90	$90.90
Purchase #2	$247.34	13.512%	$280.7606	$280.76	$280.75	$280.80
Purchase #3	$57.95	6.303%	$61.6026	$61.60	$61.60	$61.60
Purchase #4	$96.41	13.266%	$109.1998	$109.20	$109.20	$109.20
Purchase #5	$32.69	9.735%	$35.8724	$35.87	$35.85	$35.90
Purchase #6	$210.73	6.384%	$224.183	$224.18	$224.20	$224.20
Purchase #7	$42.52	10.599%	$47.0267	$47.03	$47.05	$47.00
7 purchase totals =	$775.59		$849.5652	$849.56	$849.55	$849.60