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	$14.56	3.285%	$15.0383	$15.04	$15.05	$15.00
Purchase #2	$240.56	6.374%	$255.8933	$255.89	$255.90	$255.90
Purchase #3	$114.94	4.635%	$120.2675	$120.27	$120.25	$120.30
Purchase #4	$51.34	11.566%	$57.278	$57.28	$57.30	$57.30
Purchase #5	$150.55	8.198%	$162.8921	$162.89	$162.90	$162.90
Purchase #6	$95.70	8.503%	$103.8374	$103.84	$103.85	$103.80
Purchase #7	$246.33	3.620%	$255.2471	$255.25	$255.25	$255.20
7 purchase totals =	$913.98		$970.4537	$970.46	$970.50	$970.40