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	$70.88	10.595%	$78.3897	$78.39	$78.40	$78.40
Purchase #2	$23.49	5.834%	$24.8604	$24.86	$24.85	$24.90
Purchase #3	$60.58	8.775%	$65.8959	$65.90	$65.90	$65.90
Purchase #4	$184.54	3.807%	$191.5654	$191.57	$191.55	$191.60
Purchase #5	$40.63	10.209%	$44.7779	$44.78	$44.80	$44.80
Purchase #6	$175.58	8.120%	$189.8371	$189.84	$189.85	$189.80
Purchase #7	$55.90	6.105%	$59.3127	$59.31	$59.30	$59.30
7 purchase totals =	$611.60		$654.6391	$654.65	$654.65	$654.70