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	$84.30	5.858%	$89.2383	$89.24	$89.25	$89.20
Purchase #2	$83.91	8.408%	$90.9652	$90.97	$90.95	$91.00
Purchase #3	$95.74	6.460%	$101.9248	$101.92	$101.90	$101.90
Purchase #4	$10.40	13.767%	$11.8318	$11.83	$11.85	$11.80
Purchase #5	$59.81	3.823%	$62.0965	$62.10	$62.10	$62.10
Purchase #6	$145.56	12.815%	$164.2135	$164.21	$164.20	$164.20
Purchase #7	$163.82	6.307%	$174.1521	$174.15	$174.15	$174.20
7 purchase totals =	$643.54		$694.4222	$694.42	$694.40	$694.40