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	$124.39	11.615%	$138.8379	$138.84	$138.85	$138.80
Purchase #2	$201.73	13.815%	$229.599	$229.60	$229.60	$229.60
Purchase #3	$134.31	11.739%	$150.0767	$150.08	$150.10	$150.10
Purchase #4	$201.96	7.236%	$216.5738	$216.57	$216.55	$216.60
Purchase #5	$32.89	13.683%	$37.3903	$37.39	$37.40	$37.40
Purchase #6	$140.27	10.842%	$155.4781	$155.48	$155.50	$155.50
Purchase #7	$116.70	12.860%	$131.7076	$131.71	$131.70	$131.70
7 purchase totals =	$952.25		$1,059.6634	$1,059.67	$1,059.70	$1,059.70