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	$52.51	6.524%	$55.9358	$55.94	$55.95	$55.90
Purchase #2	$234.90	12.838%	$265.0565	$265.06	$265.05	$265.10
Purchase #3	$6.45	11.759%	$7.2085	$7.21	$7.20	$7.20
Purchase #4	$136.32	3.720%	$141.3911	$141.39	$141.40	$141.40
Purchase #5	$199.43	11.371%	$222.1072	$222.11	$222.10	$222.10
Purchase #6	$209.49	5.161%	$220.3018	$220.30	$220.30	$220.30
Purchase #7	$30.57	6.383%	$32.5213	$32.52	$32.50	$32.50
7 purchase totals =	$869.67		$944.5222	$944.53	$944.50	$944.50