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	$96.53	3.322%	$99.7367	$99.74	$99.75	$99.70
Purchase #2	$131.94	11.545%	$147.1725	$147.17	$147.15	$147.20
Purchase #3	$81.55	7.556%	$87.7119	$87.71	$87.70	$87.70
Purchase #4	$216.39	3.659%	$224.3077	$224.31	$224.30	$224.30
Purchase #5	$208.78	6.522%	$222.3966	$222.40	$222.40	$222.40
Purchase #6	$143.58	11.651%	$160.3085	$160.31	$160.30	$160.30
Purchase #7	$235.98	9.636%	$258.719	$258.72	$258.70	$258.70
7 purchase totals =	$1,114.75		$1,200.3529	$1,200.36	$1,200.30	$1,200.30