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	$122.98	4.834%	$128.9249	$128.92	$128.90	$128.90
Purchase #2	$138.59	3.748%	$143.7844	$143.78	$143.80	$143.80
Purchase #3	$219.57	13.480%	$249.168	$249.17	$249.15	$249.20
Purchase #4	$131.32	8.590%	$142.6004	$142.60	$142.60	$142.60
Purchase #5	$26.26	8.683%	$28.5402	$28.54	$28.55	$28.50
Purchase #6	$232.52	4.730%	$243.5182	$243.52	$243.50	$243.50
Purchase #7	$176.54	5.688%	$186.5816	$186.58	$186.60	$186.60
7 purchase totals =	$1,047.78		$1,123.1177	$1,123.11	$1,123.10	$1,123.10