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	$98.32	3.838%	$102.0935	$102.09	$102.10	$102.10
Purchase #2	$54.83	9.210%	$59.8798	$59.88	$59.90	$59.90
Purchase #3	$140.83	7.133%	$150.8754	$150.88	$150.90	$150.90
Purchase #4	$244.87	8.396%	$265.4293	$265.43	$265.45	$265.40
Purchase #5	$238.39	12.231%	$267.5475	$267.55	$267.55	$267.50
Purchase #6	$221.77	11.439%	$247.1383	$247.14	$247.15	$247.10
Purchase #7	$172.33	6.406%	$183.3695	$183.37	$183.35	$183.40
7 purchase totals =	$1,171.34		$1,276.3333	$1,276.34	$1,276.40	$1,276.30