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	$90.73	10.563%	$100.3138	$100.31	$100.30	$100.30
Purchase #2	$197.72	6.288%	$210.1526	$210.15	$210.15	$210.20
Purchase #3	$195.54	7.677%	$210.5516	$210.55	$210.55	$210.60
Purchase #4	$209.94	5.545%	$221.5812	$221.58	$221.60	$221.60
Purchase #5	$221.74	12.779%	$250.0762	$250.08	$250.10	$250.10
Purchase #6	$182.49	5.129%	$191.8499	$191.85	$191.85	$191.80
Purchase #7	$246.61	13.649%	$280.2698	$280.27	$280.25	$280.30
7 purchase totals =	$1,344.77		$1,464.7951	$1,464.79	$1,464.80	$1,464.90