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	$33.71	4.727%	$35.3035	$35.30	$35.30	$35.30
Purchase #2	$145.81	6.161%	$154.7934	$154.79	$154.80	$154.80
Purchase #3	$41.67	13.595%	$47.335	$47.34	$47.35	$47.30
Purchase #4	$223.83	9.632%	$245.3893	$245.39	$245.40	$245.40
Purchase #5	$149.25	13.152%	$168.8794	$168.88	$168.90	$168.90
Purchase #6	$165.28	9.656%	$181.2394	$181.24	$181.25	$181.20
Purchase #7	$107.60	4.390%	$112.3236	$112.32	$112.30	$112.30
7 purchase totals =	$867.15		$945.2636	$945.26	$945.30	$945.20