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	$54.71	5.182%	$57.5451	$57.55	$57.55	$57.50
Purchase #2	$148.92	11.179%	$165.5678	$165.57	$165.55	$165.60
Purchase #3	$230.66	9.792%	$253.2462	$253.25	$253.25	$253.20
Purchase #4	$96.54	3.374%	$99.7973	$99.80	$99.80	$99.80
Purchase #5	$186.92	4.710%	$195.7239	$195.72	$195.70	$195.70
Purchase #6	$177.52	10.696%	$196.5075	$196.51	$196.50	$196.50
Purchase #7	$228.70	11.412%	$254.7992	$254.80	$254.80	$254.80
7 purchase totals =	$1,123.97		$1,223.1870	$1,223.20	$1,223.15	$1,223.10