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	$44.85	13.164%	$50.7541	$50.75	$50.75	$50.80
Purchase #2	$133.38	8.564%	$144.8027	$144.80	$144.80	$144.80
Purchase #3	$226.44	6.229%	$240.5449	$240.54	$240.55	$240.50
Purchase #4	$36.31	9.229%	$39.661	$39.66	$39.65	$39.70
Purchase #5	$88.76	12.849%	$100.1648	$100.16	$100.15	$100.20
Purchase #6	$200.77	12.196%	$225.2559	$225.26	$225.25	$225.30
Purchase #7	$93.32	8.506%	$101.2578	$101.26	$101.25	$101.30
7 purchase totals =	$823.83		$902.4412	$902.43	$902.40	$902.60