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	$75.54	3.744%	$78.3682	$78.37	$78.35	$78.40
Purchase #2	$150.39	4.213%	$156.7259	$156.73	$156.75	$156.70
Purchase #3	$243.35	7.453%	$261.4869	$261.49	$261.50	$261.50
Purchase #4	$168.27	5.120%	$176.8854	$176.89	$176.90	$176.90
Purchase #5	$210.67	13.628%	$239.3801	$239.38	$239.40	$239.40
Purchase #6	$33.61	12.140%	$37.6903	$37.69	$37.70	$37.70
Purchase #7	$70.43	9.342%	$77.0096	$77.01	$77.00	$77.00
7 purchase totals =	$952.26		$1,027.5464	$1,027.56	$1,027.60	$1,027.60