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	$66.70	3.288%	$68.8931	$68.89	$68.90	$68.90
Purchase #2	$130.38	12.261%	$146.3659	$146.37	$146.35	$146.40
Purchase #3	$106.41	6.755%	$113.598	$113.60	$113.60	$113.60
Purchase #4	$39.34	10.452%	$43.4518	$43.45	$43.45	$43.50
Purchase #5	$201.63	4.124%	$209.9452	$209.95	$209.95	$209.90
Purchase #6	$176.77	13.386%	$200.4324	$200.43	$200.45	$200.40
Purchase #7	$37.28	9.117%	$40.6788	$40.68	$40.70	$40.70
7 purchase totals =	$758.51		$823.3652	$823.37	$823.40	$823.40