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	$237.55	11.691%	$265.322	$265.32	$265.30	$265.30
Purchase #2	$102.69	7.781%	$110.6803	$110.68	$110.70	$110.70
Purchase #3	$24.98	9.179%	$27.2729	$27.27	$27.25	$27.30
Purchase #4	$80.84	5.702%	$85.4495	$85.45	$85.45	$85.40
Purchase #5	$48.94	11.480%	$54.5583	$54.56	$54.55	$54.60
Purchase #6	$124.73	11.812%	$139.4631	$139.46	$139.45	$139.50
Purchase #7	$35.70	10.525%	$39.4574	$39.46	$39.45	$39.50
7 purchase totals =	$655.43		$722.2035	$722.20	$722.15	$722.30