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	$186.67	6.314%	$198.4563	$198.46	$198.45	$198.50
Purchase #2	$126.38	5.479%	$133.3044	$133.30	$133.30	$133.30
Purchase #3	$126.80	12.400%	$142.5232	$142.52	$142.50	$142.50
Purchase #4	$250.34	9.609%	$274.3952	$274.40	$274.40	$274.40
Purchase #5	$162.80	4.236%	$169.6962	$169.70	$169.70	$169.70
Purchase #6	$80.80	11.802%	$90.336	$90.34	$90.35	$90.30
Purchase #7	$139.90	11.525%	$156.0235	$156.02	$156.00	$156.00
7 purchase totals =	$1,073.69		$1,164.7348	$1,164.74	$1,164.70	$1,164.70