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	$38.56	3.188%	$39.7893	$39.79	$39.80	$39.80
Purchase #2	$75.67	12.822%	$85.3724	$85.37	$85.35	$85.40
Purchase #3	$78.92	5.146%	$82.9812	$82.98	$83.00	$83.00
Purchase #4	$175.51	4.140%	$182.7761	$182.78	$182.80	$182.80
Purchase #5	$206.98	11.129%	$230.0148	$230.01	$230.00	$230.00
Purchase #6	$59.62	4.610%	$62.3685	$62.37	$62.35	$62.40
Purchase #7	$233.92	7.525%	$251.5225	$251.52	$251.50	$251.50
7 purchase totals =	$869.18		$934.8248	$934.82	$934.80	$934.90