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	$123.41	6.472%	$131.3971	$131.40	$131.40	$131.40
Purchase #2	$201.63	12.369%	$226.5696	$226.57	$226.55	$226.60
Purchase #3	$18.91	12.274%	$21.231	$21.23	$21.25	$21.20
Purchase #4	$78.63	4.851%	$82.4443	$82.44	$82.45	$82.40
Purchase #5	$47.81	8.119%	$51.6917	$51.69	$51.70	$51.70
Purchase #6	$240.35	6.729%	$256.5232	$256.52	$256.50	$256.50
Purchase #7	$237.99	12.383%	$267.4603	$267.46	$267.45	$267.50
7 purchase totals =	$948.73		$1,037.3172	$1,037.31	$1,037.30	$1,037.30