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	$250.46	4.314%	$261.2648	$261.26	$261.25	$261.30
Purchase #2	$36.80	12.452%	$41.3823	$41.38	$41.40	$41.40
Purchase #3	$130.71	5.822%	$138.3199	$138.32	$138.30	$138.30
Purchase #4	$144.76	11.156%	$160.9094	$160.91	$160.90	$160.90
Purchase #5	$107.78	10.122%	$118.6895	$118.69	$118.70	$118.70
Purchase #6	$151.65	11.160%	$168.5741	$168.57	$168.55	$168.60
Purchase #7	$192.61	9.779%	$211.4453	$211.45	$211.45	$211.40
7 purchase totals =	$1,014.77		$1,100.5853	$1,100.58	$1,100.55	$1,100.60