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	$118.69	8.590%	$128.8855	$128.89	$128.90	$128.90
Purchase #2	$79.43	12.824%	$89.6161	$89.62	$89.60	$89.60
Purchase #3	$114.35	12.453%	$128.59	$128.59	$128.60	$128.60
Purchase #4	$88.96	8.620%	$96.6284	$96.63	$96.65	$96.60
Purchase #5	$46.52	10.376%	$51.3469	$51.35	$51.35	$51.30
Purchase #6	$113.85	7.143%	$121.9823	$121.98	$122.00	$122.00
Purchase #7	$203.72	12.750%	$229.6943	$229.69	$229.70	$229.70
7 purchase totals =	$765.52		$846.7435	$846.75	$846.80	$846.70