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	$50.92	7.700%	$54.8408	$54.84	$54.85	$54.80
Purchase #2	$57.81	6.205%	$61.3971	$61.40	$61.40	$61.40
Purchase #3	$131.47	10.276%	$144.9799	$144.98	$145.00	$145.00
Purchase #4	$27.77	13.658%	$31.5628	$31.56	$31.55	$31.60
Purchase #5	$10.57	5.649%	$11.1671	$11.17	$11.15	$11.20
Purchase #6	$186.82	13.174%	$211.4317	$211.43	$211.45	$211.40
Purchase #7	$130.77	9.161%	$142.7498	$142.75	$142.75	$142.70
7 purchase totals =	$596.13		$658.1292	$658.13	$658.15	$658.10