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	$137.70	8.619%	$149.5684	$149.57	$149.55	$149.60
Purchase #2	$114.51	4.628%	$119.8095	$119.81	$119.80	$119.80
Purchase #3	$236.31	10.582%	$261.3163	$261.32	$261.30	$261.30
Purchase #4	$213.46	10.455%	$235.7772	$235.78	$235.80	$235.80
Purchase #5	$79.50	11.614%	$88.7331	$88.73	$88.75	$88.70
Purchase #6	$204.28	12.518%	$229.8518	$229.85	$229.85	$229.90
Purchase #7	$99.77	11.641%	$111.3842	$111.38	$111.40	$111.40
7 purchase totals =	$1,085.53		$1,196.4405	$1,196.44	$1,196.45	$1,196.50