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	$62.89	7.606%	$67.6734	$67.67	$67.65	$67.70
Purchase #2	$139.92	3.310%	$144.5514	$144.55	$144.55	$144.60
Purchase #3	$227.80	8.800%	$247.8464	$247.85	$247.85	$247.80
Purchase #4	$7.37	9.612%	$8.0784	$8.08	$8.10	$8.10
Purchase #5	$168.32	9.513%	$184.3323	$184.33	$184.35	$184.30
Purchase #6	$172.97	11.259%	$192.4447	$192.44	$192.45	$192.40
Purchase #7	$230.51	4.752%	$241.4638	$241.46	$241.45	$241.50
7 purchase totals =	$1,009.78		$1,086.3904	$1,086.38	$1,086.40	$1,086.40