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	$76.63	9.154%	$83.6447	$83.64	$83.65	$83.60
Purchase #2	$130.55	3.344%	$134.9156	$134.92	$134.90	$134.90
Purchase #3	$191.85	12.476%	$215.7852	$215.79	$215.80	$215.80
Purchase #4	$101.77	9.494%	$111.432	$111.43	$111.45	$111.40
Purchase #5	$173.82	7.840%	$187.4475	$187.45	$187.45	$187.40
Purchase #6	$29.35	12.377%	$32.9826	$32.98	$33.00	$33.00
Purchase #7	$19.43	3.515%	$20.113	$20.11	$20.10	$20.10
7 purchase totals =	$723.40		$786.3206	$786.32	$786.35	$786.20