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	$20.31	3.201%	$20.9601	$20.96	$20.95	$21.00
Purchase #2	$65.35	3.724%	$67.7836	$67.78	$67.80	$67.80
Purchase #3	$85.52	8.124%	$92.4676	$92.47	$92.45	$92.50
Purchase #4	$19.63	7.459%	$21.0942	$21.09	$21.10	$21.10
Purchase #5	$223.44	4.483%	$233.4568	$233.46	$233.45	$233.50
Purchase #6	$134.43	4.869%	$140.9754	$140.98	$141.00	$141.00
Purchase #7	$93.25	5.471%	$98.3517	$98.35	$98.35	$98.40
7 purchase totals =	$641.93		$675.0894	$675.09	$675.10	$675.30