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	$220.62	3.129%	$227.5232	$227.52	$227.50	$227.50
Purchase #2	$50.43	11.792%	$56.3767	$56.38	$56.40	$56.40
Purchase #3	$32.89	9.596%	$36.0461	$36.05	$36.05	$36.00
Purchase #4	$205.79	8.109%	$222.4775	$222.48	$222.50	$222.50
Purchase #5	$128.48	11.121%	$142.7683	$142.77	$142.75	$142.80
Purchase #6	$76.74	12.528%	$86.354	$86.35	$86.35	$86.40
Purchase #7	$50.69	11.119%	$56.3262	$56.33	$56.35	$56.30
7 purchase totals =	$765.64		$827.8720	$827.88	$827.90	$827.90