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	$121.64	8.424%	$131.887	$131.89	$131.90	$131.90
Purchase #2	$27.38	12.790%	$30.8819	$30.88	$30.90	$30.90
Purchase #3	$218.25	10.605%	$241.3954	$241.40	$241.40	$241.40
Purchase #4	$85.39	4.773%	$89.4657	$89.47	$89.45	$89.50
Purchase #5	$163.83	10.345%	$180.7782	$180.78	$180.80	$180.80
Purchase #6	$98.48	6.300%	$104.6842	$104.68	$104.70	$104.70
Purchase #7	$62.48	6.663%	$66.643	$66.64	$66.65	$66.60
7 purchase totals =	$777.45		$845.7354	$845.74	$845.80	$845.80