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	$24.32	11.618%	$27.1455	$27.15	$27.15	$27.10
Purchase #2	$206.37	11.260%	$229.6073	$229.61	$229.60	$229.60
Purchase #3	$98.54	7.267%	$105.7009	$105.70	$105.70	$105.70
Purchase #4	$110.25	6.607%	$117.5342	$117.53	$117.55	$117.50
Purchase #5	$51.73	7.421%	$55.5689	$55.57	$55.55	$55.60
Purchase #6	$134.61	12.801%	$151.8414	$151.84	$151.85	$151.80
Purchase #7	$203.51	3.387%	$210.4029	$210.40	$210.40	$210.40
7 purchase totals =	$829.33		$897.8011	$897.80	$897.80	$897.70