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	$122.59	5.142%	$128.8936	$128.89	$128.90	$128.90
Purchase #2	$236.81	13.238%	$268.1589	$268.16	$268.15	$268.20
Purchase #3	$91.48	11.617%	$102.1072	$102.11	$102.10	$102.10
Purchase #4	$87.86	9.187%	$95.9317	$95.93	$95.95	$95.90
Purchase #5	$223.65	11.144%	$248.5736	$248.57	$248.55	$248.60
Purchase #6	$237.44	13.826%	$270.2685	$270.27	$270.25	$270.30
Purchase #7	$81.59	6.144%	$86.6029	$86.60	$86.60	$86.60
7 purchase totals =	$1,081.42		$1,200.5364	$1,200.53	$1,200.50	$1,200.60