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	$107.70	3.220%	$111.1679	$111.17	$111.15	$111.20
Purchase #2	$230.41	11.284%	$256.4095	$256.41	$256.40	$256.40
Purchase #3	$75.80	5.359%	$79.8621	$79.86	$79.85	$79.90
Purchase #4	$25.73	9.331%	$28.1309	$28.13	$28.15	$28.10
Purchase #5	$52.88	9.356%	$57.8275	$57.83	$57.85	$57.80
Purchase #6	$238.25	7.298%	$255.6375	$255.64	$255.65	$255.60
Purchase #7	$55.56	12.227%	$62.3533	$62.35	$62.35	$62.40
7 purchase totals =	$786.33		$851.3887	$851.39	$851.40	$851.40