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	$51.97	6.273%	$55.2301	$55.23	$55.25	$55.20
Purchase #2	$47.32	6.463%	$50.3783	$50.38	$50.40	$50.40
Purchase #3	$214.90	7.413%	$230.8305	$230.83	$230.85	$230.80
Purchase #4	$214.86	11.780%	$240.1705	$240.17	$240.15	$240.20
Purchase #5	$35.95	13.461%	$40.7892	$40.79	$40.80	$40.80
Purchase #6	$85.98	4.179%	$89.5731	$89.57	$89.55	$89.60
Purchase #7	$80.87	7.533%	$86.9619	$86.96	$86.95	$87.00
7 purchase totals =	$731.85		$793.9336	$793.93	$793.95	$794.00