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	$34.42	8.624%	$37.3884	$37.39	$37.40	$37.40
Purchase #2	$120.39	3.661%	$124.7975	$124.80	$124.80	$124.80
Purchase #3	$81.67	12.141%	$91.5856	$91.59	$91.60	$91.60
Purchase #4	$88.63	3.689%	$91.8996	$91.90	$91.90	$91.90
Purchase #5	$96.71	6.221%	$102.7263	$102.73	$102.75	$102.70
Purchase #6	$220.46	9.716%	$241.8799	$241.88	$241.90	$241.90
Purchase #7	$228.65	11.639%	$255.2626	$255.26	$255.25	$255.30
7 purchase totals =	$870.93		$945.5399	$945.55	$945.60	$945.60