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	$125.46	8.638%	$136.2972	$136.30	$136.30	$136.30
Purchase #2	$6.32	7.785%	$6.812	$6.81	$6.80	$6.80
Purchase #3	$245.73	6.399%	$261.4543	$261.45	$261.45	$261.50
Purchase #4	$116.56	12.844%	$131.531	$131.53	$131.55	$131.50
Purchase #5	$155.96	13.135%	$176.4453	$176.45	$176.45	$176.40
Purchase #6	$234.80	11.820%	$262.5534	$262.55	$262.55	$262.60
Purchase #7	$53.49	11.221%	$59.4921	$59.49	$59.50	$59.50
7 purchase totals =	$938.32		$1,034.5853	$1,034.58	$1,034.60	$1,034.60