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	$45.74	12.722%	$51.559	$51.56	$51.55	$51.60
Purchase #2	$53.54	11.280%	$59.5793	$59.58	$59.60	$59.60
Purchase #3	$170.67	12.272%	$191.6146	$191.61	$191.60	$191.60
Purchase #4	$202.50	5.775%	$214.1944	$214.19	$214.20	$214.20
Purchase #5	$45.72	10.661%	$50.5942	$50.59	$50.60	$50.60
Purchase #6	$132.32	3.301%	$136.6879	$136.69	$136.70	$136.70
Purchase #7	$58.90	13.677%	$66.9558	$66.96	$66.95	$67.00
7 purchase totals =	$709.39		$771.1852	$771.18	$771.20	$771.30