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	$123.45	6.560%	$131.5483	$131.55	$131.55	$131.50
Purchase #2	$190.87	5.783%	$201.908	$201.91	$201.90	$201.90
Purchase #3	$211.39	12.839%	$238.5304	$238.53	$238.55	$238.50
Purchase #4	$135.54	5.448%	$142.9242	$142.92	$142.90	$142.90
Purchase #5	$238.80	8.269%	$258.5464	$258.55	$258.55	$258.50
Purchase #6	$155.77	9.530%	$170.6149	$170.61	$170.60	$170.60
Purchase #7	$55.83	12.284%	$62.6882	$62.69	$62.70	$62.70
7 purchase totals =	$1,111.65		$1,206.7604	$1,206.76	$1,206.75	$1,206.60