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	$144.79	12.411%	$162.7599	$162.76	$162.75	$162.80
Purchase #2	$34.79	9.596%	$38.1284	$38.13	$38.15	$38.10
Purchase #3	$230.82	3.347%	$238.5455	$238.55	$238.55	$238.50
Purchase #4	$97.78	12.451%	$109.9546	$109.95	$109.95	$110.00
Purchase #5	$18.82	13.814%	$21.4198	$21.42	$21.40	$21.40
Purchase #6	$9.90	13.352%	$11.2218	$11.22	$11.20	$11.20
Purchase #7	$236.71	11.535%	$264.0145	$264.01	$264.00	$264.00
7 purchase totals =	$773.61		$846.0445	$846.04	$846.00	$846.00