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	$131.79	4.509%	$137.7324	$137.73	$137.75	$137.70
Purchase #2	$176.90	8.404%	$191.7667	$191.77	$191.75	$191.80
Purchase #3	$81.76	11.234%	$90.9449	$90.94	$90.95	$90.90
Purchase #4	$140.95	9.104%	$153.7821	$153.78	$153.80	$153.80
Purchase #5	$153.48	13.838%	$174.7186	$174.72	$174.70	$174.70
Purchase #6	$25.80	12.459%	$29.0144	$29.01	$29.00	$29.00
Purchase #7	$225.92	6.372%	$240.3156	$240.32	$240.30	$240.30
7 purchase totals =	$936.60		$1,018.2747	$1,018.27	$1,018.25	$1,018.20