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	$18.31	12.303%	$20.5627	$20.56	$20.55	$20.60
Purchase #2	$84.30	9.653%	$92.4375	$92.44	$92.45	$92.40
Purchase #3	$160.59	3.129%	$165.6149	$165.61	$165.60	$165.60
Purchase #4	$226.60	7.144%	$242.7883	$242.79	$242.80	$242.80
Purchase #5	$7.61	4.368%	$7.9424	$7.94	$7.95	$7.90
Purchase #6	$175.39	4.644%	$183.5351	$183.54	$183.55	$183.50
Purchase #7	$168.89	12.473%	$189.9556	$189.96	$189.95	$190.00
7 purchase totals =	$841.69		$902.8365	$902.84	$902.85	$902.80