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	$47.32	8.786%	$51.4775	$51.48	$51.50	$51.50
Purchase #2	$182.27	4.505%	$190.4813	$190.48	$190.50	$190.50
Purchase #3	$194.39	8.872%	$211.6363	$211.64	$211.65	$211.60
Purchase #4	$109.46	9.774%	$120.1586	$120.16	$120.15	$120.20
Purchase #5	$153.40	6.218%	$162.9384	$162.94	$162.95	$162.90
Purchase #6	$128.64	11.331%	$143.2162	$143.22	$143.20	$143.20
Purchase #7	$175.37	9.323%	$191.7197	$191.72	$191.70	$191.70
7 purchase totals =	$990.85		$1,071.6280	$1,071.64	$1,071.65	$1,071.60