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	$232.73	4.554%	$243.3285	$243.33	$243.35	$243.30
Purchase #2	$37.35	7.571%	$40.1778	$40.18	$40.20	$40.20
Purchase #3	$47.44	10.610%	$52.4734	$52.47	$52.45	$52.50
Purchase #4	$40.68	13.113%	$46.0144	$46.01	$46.00	$46.00
Purchase #5	$25.90	10.373%	$28.5866	$28.59	$28.60	$28.60
Purchase #6	$186.84	13.778%	$212.5828	$212.58	$212.60	$212.60
Purchase #7	$155.33	11.639%	$173.4089	$173.41	$173.40	$173.40
7 purchase totals =	$726.27		$796.5724	$796.57	$796.60	$796.60