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	$174.28	5.229%	$183.3931	$183.39	$183.40	$183.40
Purchase #2	$158.57	5.658%	$167.5419	$167.54	$167.55	$167.50
Purchase #3	$201.43	11.292%	$224.1755	$224.18	$224.20	$224.20
Purchase #4	$30.28	4.388%	$31.6087	$31.61	$31.60	$31.60
Purchase #5	$99.47	5.484%	$104.9249	$104.92	$104.90	$104.90
Purchase #6	$44.54	5.280%	$46.8917	$46.89	$46.90	$46.90
Purchase #7	$192.31	10.413%	$212.3352	$212.34	$212.35	$212.30
7 purchase totals =	$900.88		$970.8710	$970.87	$970.90	$970.80