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	$19.44	9.438%	$21.2747	$21.27	$21.25	$21.30
Purchase #2	$134.34	5.361%	$141.542	$141.54	$141.55	$141.50
Purchase #3	$68.59	11.392%	$76.4038	$76.40	$76.40	$76.40
Purchase #4	$109.34	6.797%	$116.7718	$116.77	$116.75	$116.80
Purchase #5	$164.64	9.199%	$179.7852	$179.79	$179.80	$179.80
Purchase #6	$196.73	7.184%	$210.8631	$210.86	$210.85	$210.90
Purchase #7	$93.28	8.148%	$100.8805	$100.88	$100.90	$100.90
7 purchase totals =	$786.36		$847.5211	$847.51	$847.50	$847.60