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	$81.61	9.107%	$89.0422	$89.04	$89.05	$89.00
Purchase #2	$153.89	13.270%	$174.3112	$174.31	$174.30	$174.30
Purchase #3	$55.51	12.115%	$62.235	$62.24	$62.25	$62.20
Purchase #4	$53.62	10.383%	$59.1874	$59.19	$59.20	$59.20
Purchase #5	$248.30	5.439%	$261.805	$261.81	$261.80	$261.80
Purchase #6	$224.41	6.571%	$239.156	$239.16	$239.15	$239.20
Purchase #7	$97.91	7.364%	$105.1201	$105.12	$105.10	$105.10
7 purchase totals =	$915.25		$990.8569	$990.87	$990.85	$990.80